Again, any of these countries will be informed in no uncertain terms that they are to release their Israeli captives or face massive retaliation. So it's likely that they'll simply choose not to host them.
Retaliation?
In what way?
Throwing a nuke on belgium?
Well, that seems radical! And would be counterproductive if Israeli officials are being held there!
I think Israel would be far more likely to just take them back. Potentially immediately, given the quality of security force they would likely have on hand.
That would be the violation of our integrity and would result in a direct war.
Did Spain declare war on us when we gave political asylum to Catalan separatist leader Carles Puigdemont.
Did we bomb Iran in threatening them to release European held prisoners in Iran?
This is not how you do diplomatics, but apparently warfare is the only vocabulary you are familiar with.