Every possible circumstance is legal or illegal.
Only if you take legal and illegal to be logical opposites, but if you take 'legal' to mean explicitly allowed by law, and 'illegal' to mean explicitly forbidden, then there will be a wide and entertaining middle containing actions that are neither approved nor forbidden. People are creative and they shouldn't have restrict themselves to the list of officially approved actions or be subjected to an arbitrary and capricious legal system where the rules get made up after the fact.
Um, yeah, ASAP, if it comes before a court and a verdict hangs in the balance. If not immediately, then when? After waiting for someone to pass an ex post facto law?
No. If a case comes before the court, and the law doesn't cover the facts of the case, then the correct response is "case dismissed". If the law doesn't cover the facts then then there no way to deliver a judgement based in law. And if the judge decides to make up new rules for this case then he is *necessarily* making up rules after the fact (ex post facto) and applying those rules retrospectively.
Conversely if the public and the legislature don't like the outcome they can make a new law which will apply to future case like this one. That way you get two good things: (1) democratic government and (2) not retroactive laws.
And someone has to make up something...
No they really don't. Sometimes, even when clearly bad stuff happens, the correct response is that there is no good way to fix the problem through the legal system.