I am guessing at the moment that Ymir is still alive, just exhausted, since it seems her and Ryner have some history to settle between them. Course now I wonder if she decides to defect to the side of the scouting legion what are the repercussions she will face. Then again it doesn't seem like she has much of an affiliation with the other side so to speak since I don't think she was lying to Christa/Historia about her reason for joining the legion (i.e. looking for her). One thing I don't necessarily understand is what makes the "dumber" (for lack of a better term) titans decide whether a titan is to be considered hostile or not? I mean they just attacked Ymir, as they did Eren, and if she indeed did belong to the other side (until we get confirmation) how do they identify or decide to attack certain titans? We know Annie had some type of command that worked for her but Ymir didn't exactly do anything of the sort other than being aggressive though these titans seemed to belong to another group, the one outside, still I do wonder how they identify or decide to attack another titan how do they even distinguish one another.
One thing though is that I guess we discover something about the anatomy of a titan. It doesn't appear that not all are built big or have the potential to be big. Here is looking forward to some answers though doesn't seem Christa is that aware of what the answers actually are. So that leaves Ymir but she seems out of commission and based on how long Eren sleeps it might be for a while. Long as her side doesn't realize she may have defected or given herself away I am guessing she will be safe for the time being... Yet, given how this manga loves to toy with us I can't help but feel uneasy about Ymir and the possibility of being assassinated, from her side or possibly Ryner.
Lastly, even if the scouting legion could use her the battle potential she wields isn't that good as a titan, sure its a notch above normal scouts, any additional fire power given their losses is a plus I guess. It would be useful for a last resort option for Ymir but its not going to be very good I think against other much better deviant human type titans, e.g. large monkey guy, Annie, armored, etc. So Eren being useful is still there, I laughed when he was like "OMG my first kill as a scouting legion!", he won't need to worry about being useless anytime soon XD. Her apprehension last time makes more sense now I think part of the reason she doesn't want to fight using her titan form, other than her belonging to one side that tries to keep their existence secret, is that its just not very strong and can't exactly act like a one man army. She also doesn't appear to be utilizing any skin hardening techniques, well she didn't use any during her battle, I wonder if she is incapable or just hasn't learned? Also her limbs don't appear to have regenerated which is odd since even when Eren was ripped apart in his titan form his human form would usually be in one piece (here is hoping Ymir is still alive in off chance she is dead).