Here’s the scenario, you spend the best part of four months working with your preferred headhunter to find the ideal person for that strategically important role. Finally, everything falls into place, the candidate accepts your offer and all that remains now is for them to resign at the end of the month, serve out their notice and they will be joining you. 
Then apparent disaster strikes, the department head who was a key influencer in getting this person on board resigns. They’ve been headhunted themselves; this is the real world, it happens! Now what? How do you break the news to the top-performer who is about to join you? Will this give them the jitters to such an extent that they will walk away from the opportunity? Are you going to have to start all over and kick off a fresh search? 
This is something that I have had to deal with more than once in my time as a headhunter and it provides valuable lessons about how to approach an executive search assignment. Headhunting assignments should be thought of and managed as mini-projects. Any project manager will tell you that a key factor in successfully delivering projects is risk identification and mitigation.
So this is just another risk that needs to be managed but surely this is impossible to mitigate?
It really depends how the job has been sold to the candidate or put another way, what the candidate bought. There are always a combination of factors that influence a candidate to accept a position and understanding these is key to mitigating the risk of a change in circumstances changing their mind. There are some that are more difficult to mitigate than others, e.g. if you were to reduce the salary offered by 20% they may well be no way back. The head of department leaving will more than likely scupper the deal if this was a key influencing factor for the candidate.
This is why it is so important that you or your preferred headhunter sells the job , the key challenges to be overcome and what success looks like (above everything else). Top-performing talent is motivated primarily by what they can achieve in a role and the future opportunities that this could present. Yes of course factors such as money are important but they should never be the key driver when selling a role (to attract the best you must pay accordingly but this must not be the key motivating factor for someone to join you). Department heads and members of the leadership team could change at any given time so is it sensible to sell a role on the basis of who heads up the department currently? 
Top-performing talent knows such things are variable and they are unlikely to ‘buy’ on this basis. The key is to make sure that the key objectives for a role are linked to departmental and organisational goals. The objectives and challenges in a given role remain unchanged whoever is at the helm. A meeting with the new department head and reconfirmation of the key challenges and objectives of the role will all that will be required to get the deal back on track in most cases.
So to avoid last minute disasters, make sure your candidate is accepting the offer for the most important reason, to take on the challenges of the role, not because they “bought into the boss”.