Thank you all for the advice and opinions, this has helped me assess my options. Apologies for the delayed response.
@AndBir - I missed that ad. I've gone with @gav240z's value suggestion as a basis. Thank you. Learning that "Laid up" insurance is available is something that I'll apply to Z366.
@TobyMyers - others suggested this and after talking to the police it looks like this is the most appropriate course of action. It was too hard to prove mens rea or actus rea (guilty mind, guilty act) for malicious damage however the burden of proof for theft is possible so criminal charges are an available option.
@gilltech, @1600dave and @C.A.R. - taking no action is a valid course of action, at this stage I am still considering what action I will take.
> You'll spend years in litigation, the lawyer(s) - if you can find one to take on the case
That's true *if* I take civil action. Another option is the small claims court where I don't need a lawyer and time frames for settlement are 6 months at a maximum claim of 20K.
> move on, no guarantee you'd be ultimately successful
The process of moving on is assessing my viable options so that once I do take actions I can accept that I did everything I could to avoid having any regrets. The destruction of Z48 meant I've avoided a violent confrontation and eliminated any doubt that my brother's diagnosed and medicated mental health issues continue to worsen.
So keeping my distance was a good decision and in itself is a successful outcome, even if I don't like it, however I haven't defined what a successful outcome is in this context.
> Nothing good will come of it.
Good has come out of it. The very act of assessing my options has opened other options which lands somewhere between doing nothing and having charges laid. I am now in a much better position to decide what I am going to do as I plan the next steps.
Once again thank you to this community for the perspectives, I'll post the outcome here when the time comes.