Yes, the Mars-class impactor that formed the moon could certainly cause a re-boot of the system. Any collision that melts the crust to the depth at which the temperature was previously over about 200 C would probably have a good shot at taking out everything - but it only takes a few cells to survive. These few could hibernate in relatively unaffected rock blasted into orbit, re-entering years later after the crust had re-formed. We know this could happen because we have unmelted pieces of Mars in our hands right now.
Sure Europa will be difficult to explore - things that are worthwhile aren't necessarily easy at all. But NASA doesn't really need a crash program, they just need a consistent direction and budget to work with. Lets say the directive is "go find out if there is life in the solar system and the galaxy." This directive sets the facilities, research, manpower, launch vehicles, etc. that will be required to accomplish this in a reasonable period of time (i.e. something like 50 years, which is still fast compared to the european exploration of the western hemisphere or the building of a cathedral). If the directive is "colonize Mars" you will need a different mix of the above. The worst thing to do is to yank the NASA budget around and change priorities every four years. How much will it cost? I don't know. How long will it take? I don't know. Are these things worthwhile? Yes, I believe so because all of humanity benefits. The best way to accomplish either goal is to be persistent. Brownian motion doesn't result in any net convection - you'll just find yourself going around in circles with expensive hardware and infrastructure that eats your budget through overhead costs and doesn't accomplish what you need to do.
Pessimist: The glass is half empty. Optimist: The glass is half full. Engineer: The glass is too big.
Brad Hitch Engineer