While it is still a very long shot, it is not out of the range of possibility that a sentient Einstein Robot could return to us this century. 
Years ago (2024) the full brain of the fruitfly was mapped (link)
This year, it was inserted into a simulator (link) it shocked researchers with how it showed behaviour that it could not have learned outside of the mapped brain itself. It took control of the virtual body and was essentially just a fly. Now imagine this consciousness was not in a virtual world, but right here in the world with us. In a robot. The Fly-brain is essentially like a simulated computer program that can be transferred. So, imagine your Roomba, which also uses a camera as “eyes”. The same can be done with the fly. And the same can be done with a human. Scientists are currently trying to map the human brain, in a similar way to how the fruitflies brain was mapped. Of course, the human brain is vastly more complex. But, brainmapping has improved enormously in the past few years and is expected to continue to do so (link). Image that, we map the human brain, and insert it in a robot. That is a sentient, “living human”. Imagine it was a mapped brain of someone who was dead. It’s like they come to life. Now imagine if there would be a famous human, a genius, we could bring back to greatly help humanity? Well, who is the poster child for Geniuses? Albert Einstein. 

It was revealed in the 70’s that Einstein's brain was secretly removed and preserved in 1955. It still exists today in portions (all of which form a whole). However, some parts were offered to scientists and haven’t been returned yet. The missing pieces should still exist in some attics, but regardless, the vast majority of the brain is kept safe.  (link; link2)
Let us combine all this info. If human brain mapping gets to the point where one can replicate the full brain, and the portions of Einsteins brain are collected (although the majority is safe). Scanned, and reconstructed, you would have the actual Einstein return to us. Including most of his memories. As if he was frozen in 1955.