Especially since the original Xbox was infamous for randomly dying. Thirty years from now there will still be working NES consoles, but will there be any Xbox ones?
I don't think the original Xbox had many reliability problems though, maybe you're thinking of the Xbox 360 and its red ring of death problem?
http://breaknes.com/ (If you are interested in advanced RE, I recommend learning Russian...)
http://www.qmtpro.com/~nes/chipimages/
In other words, even if there are no original physical NES or their parts around in 30 years, relatively speaking it would be trivial to perfectly emulate one in software or hardware (e.g. an FPGA), because the functionality of the entire system is known.
A lot of sites selling new connectors claim they are made with more robust materials than the original connectors, but I'm not sure how true that is.