There must be an agreement for the case that some members of the management leave the target early. The manager’s right to obtain compensation for his shares may depend on the circumstances under which he leaves. Typically, a distinction is made as follows:

Good leavers: managers who leave the company for good reasons (e.g. in common agreement, because of dead or illness, at retirement, because some targets are reached, …); and
Bad leavers: managers who resign without good reason or who are dismissed for a certain number of reasons. These managers may have to sell their shares at less interesting conditions than the managers who leave for good reasons.

The ideal shareholders agreement would define bad & good leavers as follows:

A bad leaver is where the manager’s departure is caused by his or her resignation before the end of the … year after the completion date, or his or her dismissal for gross or willful misconduct as defined pursuant to Belgian labour law.
A good leaver is where the manager’s departure is caused by a reason other than a bad leaver, and except for the case of resignation. This includes dismissal other than for gross or willful misconduct as defined under Belgian labour law, retirement, disability, death and any other reason. A good leaver shall normally also include a manager whose departure is the result of the divestiture of a branch or subsidiary in which he or she is employed.

The good / bad leaver clause should only rule the consequences for the manager’s investment of an early termination of the manager’s collaboration. It should not affect existing termination indemnities (golden parachutes) which are purely contractual and independent from the manager’s shareholding, nor manager's investment at institutional terms (as opposed to their investment in sweet equity).