I made a massive mistake and have had stolen a relative of mines ring (long story) but it s gone and I m unlikely to get it back, he left it with me for safe keeping.

I know I can t be specific with weights ect but it was very thick and I know it was pure platinum and it had 3 whole round diamonds on it, which were pretty big. I know it was expensive but how much would you think it could be worth

Don't know enough info on quality of diamonds. Platinum along will not be that much. Your question is too vague for a answer. I doubt under $1K.

Just try a Google search, their immediate samples shoe $2000 to $10,000, maybe you can spot a photo that is a close match.

depends on qty,size,carats, clarity of diamonds, ring size, etc

yes

you wil need to see the appraisal of the item. insurance should cover theft.