OTL, he lost by one vote, but Bernard Weatherill offered to abstain as a pair with the critically ill Labour MP Sir Alfred Broughton, which would have meant a tie and a Speakers' deciding vote in favour of the government, due to an agreement with his opposite number Labour whip. The Labour whip released him from the agreement and the rest is history...
So, would this have made any difference at all?
It would have enabled Denis Healey to bring in a budget the following Tuesday. Callaghan announced in the debate that the government was to bring in a rise in pensions that November, so what other measures could Healey have introduced to try and make the government more popular?
Rumours abounded in the weeks up to the vote that Callaghan was planning a June election to co-incide with the European Parliament elections, on an anti-European platform, protesting against the influence the EEC was having on British law and the economy. Prominent Labour figures who would later become known as Euro-sceptic, such as David Owen, had already started making speeches to pave the way, and this could have been an interesting strategy - it would have forced Thatcher to either come out as a Euro-sceptic, and split the Tories who still had a huge bloc of Heathites - or made her look 'soft on Europe', which is never popular. (As it was, Europe never even featured as an issue in the 1979 campaign.)
The other option for Callaghan was to go right through to October - could he have used the summer to have patched things up with the Unions sufficiently to have clawed back some credibility as the party that could work with the unions?
Two other unknowns - would the INLA still have killed Airey Neave with no election in the immediate offing? Would David Alton have still won the Edge Hill by-election the next day?
The opinion polls did close up considerably in the immediate run up to May 3rd... I'm wondering if another month, or more likely another five months, could have closed them sufficiently to, maybe not win it for Labour, but deny Thatcher an outright win as well?
(which would have made 1979-83 look very different indeed....)