I agree with a lot of what you say, but I'll repeat myself and point out they've only known about Bobby killing Lucy for a very short time, so I think it's hard to extrapolate from that what they'd do long term.
I hope they wouldn't become part of a cover up because they're written as decent characters and it would spoil them for me. Everyone else involved either desperately loves Bobby (or Ian in Sharon's case), was intimidated into it, or has long forgotten what morals are. I can see how the writers justified it to themselves (although I find the whole cover up ludicrous), but I can't see how they could for Mick and Linda. Perhaps it's just me...![]()