Fixaflat can ruin the TPS, but I've managed not to.
The real issue is if your flat occurs in a situation where you break the bead on the rim. Or, if the tire gets torn open beyond fixaflat. But most repairs can be managed with the can of sticky stuff.
However, for what it is worth, I've now had 3 flats in the life of this car - and karma fearing me wonders why they've all been driver's rear. 1) Hit a piece of shrapnel with the GSD3's and had total sidewall destruction (runflats might not have survived either). 2) GSD3's again - must have had a nail in it - it flew out on a long downhill 50 mph lefthander. By the time I could pull over, the TPS was reading <5 psi and as it turns out the tire rolled off the rim as I pulled off the road. No fixaflat here. 3) Snow tires (currently) Dunlop wintersports - flat tire - but they're runflats - drive home, repair myself and no issues since.
When the 10 GSD3's (6 front, 4 rear) and the 8 front F1s that I own wear out, or when I chicken out, some sort of expensive summer runflat is going back on. In otherwords, in a couple of weeks I'll be having a blowout sale
And that's my spare tire theory in a beer bottle.
WW