Def speak to the embryologist at your clinic - if a embryo doesn't survive the thaw, the definition of this would be determined by your clinic (eg what % of the embryo survived). Basically, if none survived to a decent %, say 70%, a good clinic won't transfer- you would have very low chances of success but would be charged for the transfer and hospital time which would be the full cost of the FET.

Given you have a few embies, all likely at different qualities, you should speak to the embryologist about the best approach to take. You want to take as many to blast as you can ( it's expensive to do it then freeze, then do it again later to other day 3 embryos) - my question is also why didn't they take them to blast seeing that you had so many? Normally they only do day 3's these days if they only have a few because you do lose more going to blast so they want to try and make sure you have something to transfer. I have a day 3 IVF bub and a day 5 - it's sadly not as simple as saying which one to transfer as there are a few complexities to it. If you call your clinic, a decent embryologist can help you with a plan of attack for your unique circumstance, I had quite a few different stage embies so they helped me work out the best way to do it.