Ha. Hypervelocity capture has a tendency to destroy a lot of what might be interesting. For instance, one of the biosignatures we’re hoping to find are distributions of chiral amino acids that are indicative of life. Ideally we would find mostly “left handed” or mostly “right handed” forms of the amino acids in a sample as opposed to a 50:50 distribution. This would be a very strong piece of evidence in favor of the ‘biochemistry’ hypothesis. My understanding is that an orbiter will be traveling so fast as it passes through the geysers that amino acids will be broken into their constituent atoms as they’re “captured”. We’ve looked at ways of capturing them using something like an aerogel surface but more research needs to be done.

Regarding the earlier question of planetary protection, I can elaborate a bit on this process as well as we work with them a lot. Ensuring something is sterile is non-trivial. The easiest way is to simply heat it to some temperature we know kills virtually all life on earth. Depending on the systems in your probe though, it’s unlikely you can simply cook it and have it still work. Some things can be irradiated. But there are edge cases like photodetectors that can’t handle either method. For these, you can often use methods such as a vapor hydrogen peroxide, but this is a surface treatment and is probably insufficient for longer term missions to subsurface oceans. 

I work at JPL in life detection. We definitely take the search for alien life seriously. Speaking personally, not in any official JPL capacity:
Regarding the relative probability of finding life of Europa/Enceladus vs Mars, some of the thinking has to do with how long water has existed (or did exist) on the body and how much energy is dumped into the system for a potential ecosystem to use. Given that, in order of decreasing probability of an ecosystem existing (past or present): Mars, Europa, Enceladus. Mars we're actively looking at of course. Europa has many engineering challenges to overcome ( high radiation for instance). Enceladus is currently attractive because we have evidence of water ice geysers and might be able to fly through them to gather sample.