Would fitting a T-tail on the 737 Max make MCAS unnecessary?
No. A t-tail would worsen the characteristics of the airplane. While not necessarily a horrible idea in its own right, the already-nasty slow-flight/high alpha/stall characteristics of the aircraft that necessitated MCAS in the first place would make this idea dangerous. The pitch-up tendency could lead to a stall, which in a T-tail can lead to a deep stall. A deep stall is a condition in which the wing blanks the tail surfaces. Since the tail is no longer effective, recovery is EXTREMELY difficult, if not impossible. So really, a T-tail offers no advantages and may actually be MORE dangerous. Regarding your second question, no. This proposal is such a drastic departure from both the 737 and 727 that recertification would be unavoidable.