Well, we're assuming that Kennedy would have expressed interest in the Presidency. If So, I think it would be safe to assume that Tsongas would hav exited/not entered if Kennedy had expressed his intention to run.
I'd put the field at
- Jerry Brown
- Bill Clinton
- Tom Harkin
- Ted Kennedy
- Bob Kerrey
Harkin still wins his native Iowa, albeit by a much smaller margin as Kennedy fiercely competes in the caucus. With a small win in his own state and not much going for him elsewhere, Harkin eventually withdraws/fades into the abyss. Kennedy takes New Hampshire by a large margin, but Clinton still manages to come in second over Kerrey and Brown, and this is still taken as a victory. Kennedy is the front-runner, but Super Tuesday's southern-tilt in Georgia, Texas and Florida gives Clinton some victories and delegates. Unlike the actual 1992 campaign, Brown is unable to knock-off one of the two front-runners (Tsongas in the real campaign) and his campaign fails to become much of a factor, with his moderate, centrist base absorbed into the Clinton camp. Clinton could take wins in Illinois and/or Michigan, but inevitably Kennedy's momentum would have pushed Ted over the top. If Clinton stays in till the end, he probably wins California. Kennedy takes the nomination but the Dems are pushed further to the left in '92, arguably providing more room for Perot, who was leading even the moderate Clinton for the early stages of the race.