Could it possibly bring down Bitcoin if Tether implodes?
Depends on your perspective of what "bringing down" means. It is not a war of currencies out there but they are all trying to coexist and they will coexist with time because this is a democracy and not an autocracy. Currently the only use I see for tether and other stablecoins is that they can be an intermediary for doll-cost-averaging when trading at market highs or lows.
Other than that it is a fiat-pegged currency created to be a stablecoin. If there any future in it? Possible if their devs can think of something new to do with it.
Even Vitalik has expressed concerns about Tether and he doesn't fuck around
Completely your own choice to believe in it or not. Like I said, free speech is allowed and you have to use your own knowledge to determine risks and rewards.