By including Javik on the Thessia quest, we learn that the Protheans were present and helped guide early Assari development. A post quest exchange, on the Normandy, with Javik and Liara reveals that the Protheans recognized potential of the Assari and felt the Assari were the best hope for overcoming the next cycle of extinction. This final bit reveals that the Proteans, most probably, were present on Thessia during their 200-300 extinction event.
Might it not be possible for a species to escape complete extinction by secreting enough population and inert technology upon some favorable planet that already hosts a primative species? Wait for the Reapers to complete their activities and then re-emerge.
It should be possible to identify enough individuals who have never come close to reaper tech, thus ensuring there are no indoctrinated folks amongst those being placed in hiding.
Reverting to more primative ways of life and operating any necessary tech, deep underground and shielded from emissions would be doable.
Asari* Epzo 07:41, March 17, 2012 (UTC)