Best option:
1. Keep TT, and continue to groom Cardale since everyone has acknowledged he's a major project.
2. Keep TT, continue to groom Cardale, and draft a QB with the comfort level of knowing you don't "have to" draft a QB. Best time to get something in my opinion, is when you don't absolutely need it.
3. Let go of TT, sign/trade for a veteran FA QB, and go into the draft knowing you have to draft a QB.
In an ideal world, we go with #1 for now. We continue to see what we have in Cardale during the summer and into pre season, and by year 2 we should start to get an idea if Cardale will ever even be an option at QB. 2017 cap hit for TT would put him at #20 in the NFL for QB's, so the $$$ at the QB spot isn't hurting the team's cap.
If Cardale shows very little progress at QB this year during the summer and preseason, we focus on drafting TT's replacement next season (which appears to have a better QB class), and we do so knowing that we don't "have to" draft a QB b/c TT is still under contract and probably performing as expected.
In 2018 we go with TT, new rookie QB to groom, and continue to see if Cardale can improve. I believe TT's cap hit in 2018 would still only be 17th in the NFL, so we're not spending a lot of cap space at the QB position.
By 2019, either TT is setting the world on fire and we're content, or we can start to transition to the rookie QB we drafted in 2018.
Hopefully by 2019 we managed to make the playoffs in either 2017 or 2018 with TT at QB and an improved defense under McDermott.
IMO, that's a very reasonable and realistic scenario.