I was in similar situation and there was no option for me to pay to retain the use of the box for any period of time.
I think it depends if you manage to get the old box off the network before it gets the decom message, and can keep it from getting that message once restarted. Certainly I was under the impression from similar posts that it was possible but was in same position as you when I came to use to catchup.
Fortunately most were available via catchup services so little was lost.
Andy