Responses
I would like to counter you theory by saying: there isn't a tag with connection to reincarnation like 'fantasy' for example. And we already get a glimpse of the future on the first chapter which probably is old shinpei reminiscing his memories with satoko (after she died obvs) which is sad but will add angst.
Important disclaimer this is my view on the topic and I didn't mean to be rude and I applause for your positive ways of thinking
I think they will both have a tragic ending and then fast forward to the future reincarnations they finally get together, which honestly im interested to see that too