Do unused UpdraftClone tokens expire?

No. Once you have purchased UpdraftClone tokens, they remain on your account until they are used.

The only exception to this is if no activity happens on your account for some years (no logins, no purchases, no use of UpdraftClone, UpdraftVault, UpdraftCentral, etc.), then for data privacy reasons you may eventually be deemed an ex-customer, and your account deleted.