Well, Mother Brain also noted that the Planet will recover, given enough time..
That seems to mean that the Entity will survive, although humans will not...
I generally take the Entity to be a manifestation of the
Gaia Hypothesis. The Entity isn't just the planet; it is the life of the planet. If Lavos had fallen on a lifeless world, it might have been able to siphon a little energy, but it is a living planet that provides a banquet. The entity isn't just the rocks and minerals, but also the flora and fauna. Humans, then, are a part of the Entity, similarly as how liver cells are part of the human body.
Thus, as long as the possibility of life is maintained on a planet, the Entity (of that planet) wouldn't die, but it wouldn't be the same creature either. I suspect that Lavos would have left the Entity crippled by its disease, as it were, similarly to how a human might be crippled by a serious illness.
To note, Saelind, Schala and Lavos can't be the Entity. Schala because she wasn't in the DBT when the events of CT happened (while the DBT might have a different flow of time, by all apperances Time Error still flows there). Lavos because CC specifically state that he was pissed off at being defeated by Crono and Co (hence why he pulled Chronopolis into the past; to prevent his own defeat).
