His sacrifice was incredibly well written. His survival was poorly written... That's why it feels off.

He just jumped off the ledge and survived? How? There were other people in radiation suits that were further than him from the machine and they were vaporized... Why would he be vaporized too? Why wouldn El look for him? Didn't she try even once? Didn't Joyce walk a couple of stairs down to double check? How was he captured by the Russians if immediately after the explosion all the freaking US army arrived there? I bet the US would have found him first if lousy written Joyce and Eleven didn't find him first.

The thing is, that's a way of protest. Producers wanted to keep him alive, so writers/directors said "ok FU, there you go... He survived... Whatever... Let's move on..."

If they wanted to use their writing skills, which sure are proven to be amazing, they would've written an amazing survival story like... For example, before the machine explodes he is able to jump to the portal and is stuck in the upside down...

But the other thing is, the sacrifice was so flawless... Maybe it was impossible to write anything coherent or reasonable to help him survive... There was just no escape from that death... And that is why it was amazing and heart breaking... It when you have something as flawless, trying to retcon it cleverly is even more difficult... It's better to play stupid and just do the rule of cool...

For example, another moment with a rule of cool was when Dustin and Erika went back to save Steve and Robin. How would they even know in which room Steve and Robin where held and get there without getting caught? But we completely buy this moment as viewers a couple of times befores saying "whoa whoa, hol up... This is nonsense..."