The machsim licenses are perpetual within a single version, but will only work in the next version until the end of their maintenance cycle. So if the client happens to update during the PY maintenance cycle, they'll be fine, if they're already expired, they will not be able to use the existing key in the new mastercam version.

Link below to spreadsheet for keeping machsim license keys provided by Postability and IHS.

Machsim License Keys MC2022+