Sprint being purchased by a "bigger company" would be a very bad thing. What other "bigger company" would want a CDMA carrier but Verizon
?
I'd have no choice but to go with a GSM carrier and buy new devices the moment a Sprint/Verizon merger was finalized. No way I'd be a Verizon
(device lock down) customer.
For a larger GSM carrier to buy Sprint would probably be a real pain, given the fundamental network differences. So I doubt any GSM carrier would want to, but I guess anything could happen.