Any post on this thread should refer to the country whose law applies. The rules differ between UK, USA and Canada.

Nigel's comment that there is no such thing as a post dated cheque is technically correct (UK).

The law changed in 1992 and I don't know if they changed the definition of a cheque then but previously the formal definition was "a bill of exchange drawn on a bank and payable on demand". If it is post dated it isn't payable on demand therefore it isn't a cheque. The fact that a bank's pre-printed cheque form has been used doesn't make it a cheque in law until it falls within date.

If the drawer dies in the meantime then the payee has a claim against the estate and will need to obtain a new cheque from the executor if there is a will or administrator if there isn't.