Put together a separation package that works for everyone.

Something like:

* Last day of work is today, all building and system access is revoked.

* Remain employed, on the payroll, full benefits, etc until after vesting (30, 60, etc days).

* Subject to signing an agreement around non-disparagement of the company, not poaching employees, etc, whatever else.

These kinds of things are typical for layoff situations. Trying terminate prior to vesting seems unnecessarily punitive, but you can still get them out of the building immediately.