They should do something to make the recent active PD players so they will be interested to continue their gambling habit in Stake, otherwise they may try to find an alternative because they may disappointed if there is no offer at all.
It would be fair if PrimeDice users could transfer their VIP level to Stake.com. Signing up on Stake and other casinos is the same if Primedice doesn't allow transferring their VIP level to Stake. There is very little to no chance of transferring VIP level, considering the stake is already a giant casino. They don't need new players. Stake is full of whales.
Some old players may come back in the future, and they would be disappointed to learn that PrimeDice has closed its operations. The team would keep the domain for a long time, so they can forward players to Stake.