If you have a handheld, then you can use that. Alternatively, if you need to stick it in a field/divert to a strip and land no radio, then do that first and then telephone the ATC unit you were speaking to.
Personally, speaking as someone who works with electrickery and electronic gubbery of various sorts, and having experienced electrical fires (thankfully on the test bench, not in the air
), including a power supply that blew up almost in my face sending two-foot flames shooting into the air (big capacitors y'see
), very good idea to kill the power straight away and extinguish the flames. Fire doesn't take long to spread at all.
Prioritise. Deal with the circumstance, then talk.