Given that it's been blocked at EU level on competition grounds, it would be foolish to plan to offload the shareholding to Ryanair. It would end up taking longer, even if it's possible and would herald a period of uncertainty that would see the value of the asset decline.
JetBlue or Etihad is a tricky one. JetBlue are more likely to be happy to see Aer Lingus just get on with things, particularly in short-haul and are unlikely to want to invest just to get their hands on Heathrow slots. However, I believe the government are obliged to sell to the highest bidder (once it's OK within EU and US ownership rules, which given the other shareholdings, Etihad should be).