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This is article one of seven in our Sustainable M&A series
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Published
9 July 2026
The deal logic was sound. The synergies were modelled, the value quantified, the integration plan approved. But eighteen months later, the numbers tell a different story, and nobody can point to the exact moment it went wrong.
Maybe that is because there was no such moment. Value in M&A rarely disappears in a single failure. It leaks – through an organisation that was never set up to deliver what the model assumed, through structures misaligned with the deal ambition, through critical people leaving at the wrong time, through culture friction slowing every decision by a week, through employee experiences that produce confusion where the plan assumed clarity.
Earlier this year, we addressed decision debt – the accumulated cost of postponed and poorly made integration decisions – and the six People & Organisation moves that separate deal closed from deal delivered. Since then, the market has only raised the stakes: 2026 is on track to be a record year by value, but concentrated in fewer, far larger transactions.
The integration load is not spreading but stacking. So, in this article series, we go a level deeper to focus on where the leak actually starts and how to run each area in practice.
The mental model behind the leak
Here's what makes value leakage stubborn: it isn't caused by ignorance. Ask any deal team whether people matter and you get an immediate, sincere ‘yes’. Leadership alignment, retention, culture, communication – every leader can recite the list.
The cause sits one level down, in how the work is organised. In most deals, the people agenda is set up as a workstream: a box on the programme chart, staffed by HR, activated after signing, running in parallel to ‘the real work.’
P&O is the thread that runs through the entire deal
A workstream starts when someone activates it. A thread is woven in from the first page of the financial model – or it's missing, and the fabric unravels under load.
Across integrations, we see the thread break at three specific moments:
The synergy window closes whether you act or not
The timing gap punishes hardest, because the value in the deal model is perishable. Every synergy case implicitly assumes capture within a window. Three forces close that window on their own schedule, all of them people mechanisms:
- Talent walks
Acquired employees leave in year one at nearly three times the rate of direct hires – roughly one in three. The people on whom the revenue synergies depended are gone by month eight, and no revised plan brings them back. - Habits harden
In the first weeks, both organisations are unusually ready for change – people expect it and accept it. A quarter in, the ‘interim’ state has become the de facto state: shadow structures form, workarounds calcify, and every later change costs double because you are now undoing something. - Attention moves on
Leadership focus, board patience, and integration budgets are frontloaded. A synergy not captured before the organisation declares ‘back to business’ rarely gets captured at all. It is not formally cancelled; it simply expires.
This is what connects the three forces to the cost at the centre: decision debt is the cost accruing inside the window. The window is the deadline that makes the debt expensive.
The evidence is clear
The research points in one direction: deal value is rarely lost because leaders lack ambition but because the organisation is not ready to deliver it. Only 24% of acquirers have a near-complete value creation plan and fewer than half have a process in place to track synergy delivery. At the same time, the people the value case depends on start moving fast: acquired employees leave in the first year at almost three times the rate of comparable hires, and around 40% of critical talent is lost within 18–24 months post-transaction.
The outcome is predictable: only 14% of companies achieve full success across strategic, operational, and financial deal goals. In other words, the value case is often modelled before the delivery system is built, and before the people needed to deliver it are secured. The question is not whether people matter in M&A. Everyone agrees they do. The question is rather whether your organisation can convert deal ambition into delivery through people – in the right sequence, at the right time.
Six questions this series will answer
Across the lifecycle – due diligence, sign-to-close, integration, handover to operations – the P&O work of a deal falls into six areas.
Over the coming period, we will dive into each of these areas:
- Structuring the organisation – How integrated do you actually intend to be?
Absorption, preservation, symbiosis: the integration strategy you choose determines the scope of every P&O decision that follows, but most teams never make the choice explicitly. - Sustainable workforce optimisation – In what order do you make workforce decisions?
Why the sequence matters more than the numbers, and what to lock down before any reduction is announced. - Building sustainable culture – Where will the two cultures actually meet?
Culture does not clash in the abstract; it clashes in specific moments – decision forums, escalations, performance conversations. How to find those moments early and manage them deliberately. - People tech enablement – Can the people systems carry the organisation you just designed?
A new operating model is a set of promises – that people can be hired, paid, moved, measured, and developed from day one. People tech runs deeper than payroll and master data, determining whether the new organisation can grow into the deal's ambition. - People function harmonisation – Do employees meet one company or two?
Aligning the HR machinery – processes, performance, policies, reward – so the answer does not depend on where someone sits. - Sustainable employee experience – What does the integration feel like from the receiving end?
Onboarding, communication, and listening designed for the people the deal happens to – one employee at a time.
The takeaway
Deals do not fail from lack of intent, and rarely from lack of a plan. They fail because value leaked through an organisation managed as parallel workstreams instead of one connected system, while the synergy window quietly closed.
If a transaction is on your horizon, the cheapest moment to find the leaks is before they start. That is what the next six articles are for – and what we do for a living.
