I would be most concerned over the lock coming out and locking on you. IDK what's left of your system, but if the lock is there, I'd look for some way to make sure that doesn't kick in.
The problem with using switches, is that you'd be cutting the wires or tapping into the wires. If you don't do it right, it can cause damage.
Otherwise, I'd say go for it. If they just jacked up the key part, maybe you can use a screw driver to operate it, I did that with a car before.
My concern with an aftermarket would be quality. I wouldn't want it to cut out at the wrong time or not pass the proper amps.
What about a used OEM one parting out from eBay? It would be a different key, but maybe you can get a set for the seat if that matters. There should be some for sale somewhere. Motorcycle junk yards? Are they the same as... RC51, Fireblade... How different can these things be?