It seems that my initial reaction was correct, Lomenzo quit the band very suddenly, leaving Megadeth in urgent need of a bass player - this quote just went up on Blabbermouth:
Bassist David Ellefson spoke exclusively with U.K.'s Classic Rock magazine about his return to MEGADETH after an eight-year absence.
"It literally happened over the weekend," he said. "And I can hardly believe it myself. There was clearly gonna be a change in the lineup, because James Lomenzo was leaving. Dave [Mustaine, MEGADETH mainman] and I talked on the phone, and all the feuds, all the arguments we've been having over the years just melted away. It just goes to show what direct contact can achieve!"
Regarding how the whole thing came about, Ellefson said, "Obviously, I have no clue what happened within the band. But I got a text from Shawn [Drover, drums] and it just said, 'If ever there was a time for you and Dave to talk, now is it.' It's one of those messages you act on immediately. Typically of MEGADETH, things then happened big and fast.
"In all honesty, talking to Dave again was wonderful. It was the right thing at the right time, done in the right spirit."
Weeeeeeelllllll, he would say that, wouldn't he? We'll just wait and see if he is still in the band when the next album gets written. That said, if as suggested, the 20th Anniversary RIP tour comes to England with Testament and Exodus, I'll definitely be there.