No concessions would ever have been enough for the European Research Group, unfortunately. If we end up leaving without a deal, the economic crisis will do for the government. If the ultras are defeated and they manage to scrape a compromise through, they'll take her down with them.
Still, May has proved remarkably tenacious - we all thought she was finished multiple times and here she still is. If she does still want to cling on to power a little longer (which surely must be a big if at this point...), she'll seek an A50 extension. This would be fairly consistent with her behaviour thus far, and is also probably necessary to pass the required amount of legislation anyway.