I'm not in favor or trading Gray, but I don't think he's a workhorse, he pitches fewer innings per start than Ryan, Lopez and Ober. And for good reason, he does start to wear down earlier in games. He hasn't gone 7 innings since April.
It's also not exactly a 1st round pick they get, it comes after the first round, something like pick 33-40. But that's only if Gray signs for 50M+. Say teams shy away from his age and he only gets 2 years at 20M each, than the Twins pick would come AFTER the second round.
That said, if the Twins traded Gray and got a controllable young starter in return that could be plugged into the 5th spot into the rotation right now, I'd listen.