With the Hawk-Eye debate, I cannot see how it will be possible to sue for an error in another match (well any match for that matter).
I may be wrong, but I'm pretty sure Hawk-Eye don't market themselves as being absolutely 100% guaranteed correct all of the time, hence for example Umpires Call in cricket - there is always a margin of error.
Unfortunately mistakes are going to be made in life, with or without VAR, and with or without goal line technology.
If Bournemouth go ahead with this legal action and are successful then a huge can of worms is opened, what's stopping other clubs suing for similar mistakes, or even individual referees for poor decisions - who makes the decision if they were right or wrong? A Judge?
I really hope they see sense and don't go ahead with this.