If you have the three-and-one debate format in 1980, I think Reagan is still the ultimate beneficiary. Likely you'll see again each presidential debate with a set theme: domestic issues/economy, foreign policy, catch-all.
Carter's going to benefit from having time to respond to Reagan's attacks, but Reagan's going to have even more time to make his case to millions of Americans. Bush/Mondale is going to be a wash since no one really ever decides these things based on the VP debates. (Remember how Quayle got thumped in 1988 and it made exactly NO difference in the outcome?)
I'd say it breaks down like this:
Debate 1: Domestic Policy - Reagan, edge
Carter attacks Reagan on social security, medicare, and generally being too much like Barry Goldwater. Reagan effectively counters the attacks with "There you go again," while attacking Carter's failed stewardship of the economy. Failed leadership arguments bring to mind the failures elsewhere in the Carter administration, which Carter can't discuss. Reagan comes out, slightly, ahead.
Debate 2: Catch-All - Carter, edge
The Catch-All debate might make more sense as the wrap-up, but neither side wants to have the foreign policy debate too soon. Carter doesn't want Reagan to attack his failures in Iran and other parts of the globe, and Reagan wants to wait to make that exact case until the end of October. It's a risky move for Reagan. If Carter gets the hostages released over the next few weeks, it could mean the election. On the other hand, if Carter fails then the payoff is huge.
The actual debate is kind of blah. In his second performance, Reagan fails to exude the sunniness that has characterized his campaign to this point, and Carter is Carter. Reagan starts setting the theme for his attacks on the Carter foreign policy. Carter rebuts some of Reagan's misstatements from the last debate and attacks Reagan's hawkish, inflammatory rhetoric. Carter wins by a hair.
Debate 3: Foreign Policy - Reagan, decisive
Reagan's gamble has paid off. The hostages haven't been released, and Carter just looks TIRED there on stage as Reagan has regained his poise. Carter makes an unforced error with the "my daughter Amy" bit, since this is the first debate which actually raises the issue of nuclear weapons. Carter looks and talks like a president who's about to lose; if it looks like a duck and quacks like a duck, it's probably a duck. Reagan scores a decisive victory.
VP Debate: Catch-All - Tie; possible Bush, edge
Between the second and third debates Bush and Mondale meet for a catch-all debate. Bush scores on the foreign policy arguments, Mondale scores on bringing up Bush's old line of "Voodoo economics." America collectively yawns. Bush probably won by a hair, but who honestly cares in this debate between bespectacled, charisma negative running mates?
Impact
Reagan still comes out ahead of Carter, but the election is closer. The CPB is formed ahead of schedule since the campaigns are pretty much calling the shots anyhow.