Cultural mismatch can be a difficult thing to overcome, but as with all challenges, it is not impossible. The largest negative impact to cultural integration failure would likely be loss of employees, loss of customers, and eventually loss of the synergies and goals of the deal in the first place. Effective change management can overcome cultural challenges, if they are well planned for in a realistic manner. Not everyone will get on board if culture changes are significant, but with the right plan and attitude, shift is possible. I witnessed this in an integration of a large national for profit acquiring a regional non-for-profit, and saw first hand what worked and what did not. It definitely takes careful planning, patience, and strong, caring leadership to guide both organizations through this. Respect, caring, and honesty go a long way.