No, they responded with a lowball offer because they feel the OP is motivated to sell at any price.
His best bet is simply not to sell and to wait for them to make an offer.
OP is confused about the shareholder and employee roles, they are not linked other than through vesting and the shareholder agreement (which they have presumably signed).
He can easily quit as an employee while remaining a shareholder in the company. Those roles need not be connected forever and there usually are - vesting excepted - penalty free ways of stepping out of a company while you keep whatever shares you already have. Clawbacks in a situation like that are very rare.
His best bet is simply not to sell and to wait for them to make an offer.
OP is confused about the shareholder and employee roles, they are not linked other than through vesting and the shareholder agreement (which they have presumably signed).
He can easily quit as an employee while remaining a shareholder in the company. Those roles need not be connected forever and there usually are - vesting excepted - penalty free ways of stepping out of a company while you keep whatever shares you already have. Clawbacks in a situation like that are very rare.