There are various random claims of proof of something happening after death, contradictory and with no real evidence. When there's no evidence, and people make very contradictory claims while claiming absolute evidence but having now, .... it's probable that there's nothing happening. I'd like to imagine my deceased loved ones are still around somewhere, but I don't think they are.
I take the position that Jesus is that authoritative eye witness — the whole Christian religion hinges on that. I find his claims, the historical documents, and eye witness testimony that’s been preserved from the 1st century too compelling.
It's possible that there is nothing (the dreamless sleep was just Sagan being poetic I would guess). It's also possible one or more of the many religions are correct.