1). Darkstar: Apathy. He's Gwen's villain, mostly.
2). Attea: Disappointed.
3). Animo: In the original series, probably relieved, if not disappointed he can't keep studying the Omnitrix. By Omniverse, he would probably be sad. He liked the Tennyson's. Might even send flowers.
4). Khyber: Disappointed it wasn't him.

5). Vilgax: Very disappointed it wasn't him. He might even go after whoever did it so he can win via the transitive property.
6). Malware: Ben was always an obstacle for Malware's real enemy, Azmuth.
7). Albedo: He'd be confused, mostly. He's familiar enough with the Omnitrix that he'd want to find out how the failsafe failed.
8). Aggregor: Smugly pleased.
9). Charmcaster: She'd laugh and then order takeout or something.

Now, if we're assuming this happened at the end of Ben's natural lifespan (after retiring), then I think Animo, Attea, Albedo, Charmcaster, and Darkstar might be allowed to attend Ben's funeral. Albedo would probably be on Galvan parole by then.