Business Ownership: Can Shares Be Cancelled if Not Vested by a Leaving Founder of a Startup

My question involves business law in the state of: California

Hi There,
I have a founder who is leaving our company and we agreed to provide him with 5% of the company (he would have been entitled to 3%) as a severance to ensure a smooth transition.

When we formed the company we all paid x dollars per share of the company, however had a 5 year vesting schedule for restricted shares. When reading through the contract I noticed that we do not have a "repurchase plan" set up in the contract, however the verbiage reads something to the affect of "if you do not vest your shares you do not receive your shares". We were advised by a lawyer consultant that our leaving partners shares could just be "cancelled", however I don't understand if that is possible or not. Everything I look through and read says that we have to buy the shares back since he owns them at this point.

Is it possible that the shares can just be "cancelled", and if so, what are the mechanics behind the cancellation of the shares?

Thanks!!

Business Ownership: Can Shares Be Cancelled if Not Vested by a Leaving Founder of a Startup