My option is that as long as there is not any sponsor nor billionaire paying the usual loads of money to go, he's not doing the travel, doesn't matters if the HOF inducts DS or him as a solo artist.
My hats of to Illsley, Clark and Fletcher to show their respect to the band fans going.
I don't think money is the only reason why he won't attend the ceremony. It won't cost him a fortune to go there. I can go there if I think it's worth a visit, and I guess you, too. And apparently he has much more money than you and me.
And I still doubt he will attend the ceremony if RRHOF covers all his flight tickes and acommodation there.
And remember, he is the man who does not like being in the spotlight, as well.
I think the main reason is still the relation between him and some other ex-member(s).
It's obvious that it is more likely he will be there if he still keeps good relations with all other ex-members. In that case, there would have been no song of "Terminal of Tribute to".