my first jedi knight was a sentinel. i finished chapter 1 with her, then noticed that i really didn't feel like using her anymore after that. eventually, i deleted her and rerolled her as a guardian tank. best. choice. ever.
i have a sage healer as well. i don't find her dying very much, or at all for that matter. i can solo heroics with Qyzen tanking pretty easily. you're sending in your companion first, right? using cc? bubble yourself? the new self heal helps a lot too. just make sure to keep your companion well geared as they're the one who'll be doing the brunt work.
i'd hold onto the sage for now, even if you don't play it. if worst comes to worst, you could always respec him to DPS instead.
thats interesting story and thanks for the advice there is just one small problem I got impatient and didnt think anyone was gonna reply to this thread so I kind of already deleted him and im slowly reworking him as a shadow sorry