I know when I rooted around under my tank the loom needed some serious tidying. up, removed all the crap and went keyless, found a few aux cables that were not required. There could still be an electrical issue in yours rather than ECU, maybe an auto electrician to do loom check? What you need to remember is power goes from battery via a fuse to fuse box then rest of bike, only power that comes from bike would be alternator to battery, so for ECU to get a power surge enough to fry it, it would mean it would have to possibly come from that broken wire back to ECU, which im slightly curious about, plus the ECU would be dead, dead, rather than letting it run rough, when I fried mine there was a horrible smell of burnt plastic from it and it was dead. Im not doubting the mechs, im just questioning the reasoning