Probably not an ally or a friend coming, but likely Kizaru IMO. The Gorousei must've asked Akainu to send an admiral since they know Imu is nerfed outside Mariejois.
Not sure where I saw this but... since someone will make an Enel kinda face this chapter, it seems maybe Luffy is fine and somehow fooled Imu with some reality bending shit or something, or it could just be from the Sanji or Zoro fight. Anyway, Sanji/Zoro fight is nowhere near the end, and Gunko is likely to battle the strawhats again or start her own flashback, so if someone really was coming to save the day, they're probably a bit too early since the loose ends aren't settled, unless Luffy is donzo and needs help immediately. My guesses would be either Shamrock or Kizaru.