They almost certainly had flight spares but with two weeks until your launch window, there is zero chance you are deintegrating multiple systems, swapping in the spare, reintegrating, and re running your acceptance test campaigns. And that is assuming that they damaged a subsystem. Back powering the entire spacecraft could have wrecked your power system and anything connected to it. You'd have to disposition every part of the system that was touched. It's much more involved than just swapping in the spare and sending it.
The implied context here is that you'd forgo the usual tests, because the alternative is to send nothing to Mars.
According to Wikipedia they could have stretched those 2 weeks to around 3 weeks, but after that they'd have missed the launch window.
The usual processes are there to have a near-certainty of a working rover, but under these circumstances I'd think they'd just YOLO it and hope for the best.
But that assumes they've got spare electrical components, or alternatively a better use for the booster sitting on the pad than such an improvised mission.
Spirit/Opportunity had the SSTB1 test rover, which supposedly had a complete set of scientific instruments. If it was fully qualified and tested, swapping it out could have been as easy as dropping it in the lander and writing a different serial number in the paperwork.
(I really doubt it was fully tested. But why else have a flight spare vehicle?)
