IMO, it's not about this person. It's about the rest of the team and the message you want them to take away. Letting someone go right before they vest will likely create distrust on the rest of the team.
Typically, vesting cliffs are designed to give some breathing room for new hires. If they turn out to be terrible, you can part ways with them without impacting your cap table. If this person had long term performance issues, it's kind of shitty to wait until just before they vest.
I don't know what your company's situation is, but this likely doesn't have to be an "all vesting" or "no vesting" situation. By default, it sounds like you can terminate this employee and provide "no vesting". You can make it clear that you'll be offering them some/most/all of their anticipated vested stock despite you terminating their employment prior to the vesting cliff. This lets you terminate the relationship right now while saving face with the rest of the team.
Typically, vesting cliffs are designed to give some breathing room for new hires. If they turn out to be terrible, you can part ways with them without impacting your cap table. If this person had long term performance issues, it's kind of shitty to wait until just before they vest.
I don't know what your company's situation is, but this likely doesn't have to be an "all vesting" or "no vesting" situation. By default, it sounds like you can terminate this employee and provide "no vesting". You can make it clear that you'll be offering them some/most/all of their anticipated vested stock despite you terminating their employment prior to the vesting cliff. This lets you terminate the relationship right now while saving face with the rest of the team.