I see Tom as loyal to the bitter end. Even if he was hurt, bitter or angry at Michael (as brothers occasionally are sometimes) he never would have done anything against Michael or Michael's family. Although Tom's view of Michael as a brother is not always reciprocated, Tom certainly was viewed as a brother by Sonny and Fredo and perhaps as a son by Vito and Mama Corleone.

So Tom would be loyal to Vito's memory if nothing else.

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.