Did Mercedes deserve her fate?

Not really, she thought he was dead. It's okay to move on if your loved one is dead.
I mean, she did say she'd kill herself if Fernando murdered him, but that was more like a counter-incentive, right? Also she said Dantes right again at the end.
Also, her fate wasn't all that bad, all things considered:
>happy youth
>rich nobleman's wife
>majority of life in wealth
>even after shameful death of said husband, she gets to live a comfortable life and see her son grow up.

>>7656925
set* Dantes right.

>>7656925
But she spent 10 years mourning her betrothed then married a man she did not love out of necessity. And then when Dantes returned everything was taken from her, and she commits herself to a lonely life deprived of both wealth and poverty.

>>7656962
Still better than what Dantes had to go through.