Here's the closest analogy I can think of.
I play reed instruments: clarinet, saxophone of various sizes and to various levels.  At one point in learning Bb soprano clarinet I switched from soft, mushy, easy-to-play beginner reeds to stiffer, squeakier, richer grown-up reeds.  Actually, it made my range grow into higher notes and improved resonance throughout so not exactly the same but pretty close.
It wasn't like learning to play again from scratch, but I sounded horrible for a couple weeks.  Make that a couple months, and that's what T does to your voice.  Richer resonance, much lower floor, squeeeaky.
A lot of guys give up on singing during this time.  There's nothing that says you have to.  Your voice will be different, but still you.  Just you as a guy.  I can't promise anything, but I do not think that's what you will consider "ruined."