I have no idea of how long it has been researched - to summarise
1: there would appear to be a marriage
2: the query has been posted elsewhere (? where) with presumeably no positive response
3: the originator is not 100% sure it was the Isle of Man.
4: there is no obvious burial record after diligent search and General Registry cannot find one (on past experience this does not make it 100% certain that there is no such record)
5: the local papers have been checked ? and no such death reported though any such inquest would certainly be reported.

sounds like a lost cause