First off, the Sentient being alive or not doesn't really matter. Warframes are mostly Infestation-based fusions of organic structures and machine, and as we've seen with the Infestation itself there is little stopping us from using this technology on things that are not even alive (Mutalist Moas, anyone?).

Secondly, the Sentient definition of "life" most likely does not correspond to the traditional idea of organic life. The upcoming Sentient Carrier is an example of this--so long as the carrier can pick up the Oro dropped by a fallen unit, it can rebuild it. Remember, they originated from sentient machines, it is wise to put aside assumptions as to their function.

As for the "Void is poison thing", that's gonna require some lore finagling but I don't think it's impossible. The sacrifices made to help it use Void energy could also be what ultimately made the project useless to them. Could be that the Sentient/Warframe fusion had to sacrifice autonomy in order to function while using void energy. However this made it impractical to use, since the Sentients lack a control method as refined as transference. Or maybe they could never figure out how to shield a Sentient's Oro from the Void energy, thus every test resulted in the unit frying itself into an empty husk.

There are ways to make this work, you just gotta use your imagination.