I know that it's the unit that is regulated, but people are effectively declared "inelligible" all the time ( eviction for non primary residence is an example. Those tenants evicted have a difficult time finding an apartment for the same rent).
Rent reg's exist to keep people in the city who otherwise could't afford it. When someone is able to buy property in another location it is a strong indication that they could afford higher rent. I just think it is wrong (and greedy) to ask another private party to essentially subsidize the purchase.
You are right, a lndlord most likely won't forgive rent due to hardship, but how many tenents would pay more rent to a landlord who is having trouble? I can't think of any group in our society that will forgive debt out of the kindness of their hearts, (home loans, auto loans etc.).
Also, people buying property outside of NYC hurts our tax base. It would be better if those home buyer's spent their money in the city, weather through home purchases here or through higher rents.