RIO worries

hi,
what is happening to those RIO when theirs double-seat planes are replaced by new single seat planes. For example, from f-4/14 to f-18A/C/F, or Tornado to Eurofighter. Are they retired ? or are they converted to real pilot if young ?

Another question is from where RIO for those planes (particularly like F-16D block 50, Su-30xx) come. I mean are they fresh pilots ? maybe they are moved from single seaters like block 30 for example. I so, i think it is not especially good for them.

sorry if question is simple to answer 😉 .