You do not have that client anymore.
Unfortunately and sadly, they are deceased, gone.
Like the “Norwegian Blue”, they are an ex-client.
(Dead Parrot sketch - Wikipedia)
(Dead Parrot Sketch (the original) - YouTube)
Any POA that you have on file for this ex-client has been cancelled on DOD.
For your acceptance of a new client, you should have all protocols in place as to verifying their identity (required), and hard evidence of any purported legal authorities they are asserting they may have.
It may be that you would want to work with relevant parties, such as estate lawyer, additional parties etc, that the verified (proven) executor may hire.
Are you going to be hired as estate accountant? Estate tax preparer? For Final T1s? For T3s? The executor would need to arrange all that.
Although in the real world, people (other than lawyers) sometimes take shortcuts, every shortcut carries problematic risks…
Not every Will gets probated, but that is the “gold standard”, being the evidence of the Court being satisfied as to the validity.