Thank you very much for the info, do you remember at what temps where they exposed when they died?
Like most tropicals I grow, they don't die after a single night of cold, after all we only go to -3 few night, but they die because they cannot stand a prolonged period of cold.
Even Muntingia Calabura outside have no problem handling some night at -3, but if you leave it the whole winter it will die eventually.
In fact Cas Guava has around 2 cm of green cambium at the base, only on one side the side not exposed to the wind.
I doubt it will recover however, probably will continue rotting down even if we have almost summer weather since 1 month.
Many times however if you manage to get the plants to pass the first winter in ground it will suffer less the next winter, such is the case for example of my malaysian red guava, that was burned down to 3-4cm from the ground last year where the wood was around 3cm, while this year it didn't even burn 8mm wood and we had considerably more cold nights.