I agree that industrial unrest was the main reason why the Conservatives won the 1979 General Election. But it was not the only reason.
Immigration (as now) was a factor and the Conservatives exploited public unease about the levels of immigration from the Caribbean and the Indian sub-continent. Mrs Thatcher indeed made a reference to Britain "being swamped by people of an alien culture". During the 1970s, the National Front had made inroads into the Labour core working-class vote by exploiting concerns about immigration and the Conservatives capitalised on this.
The Troubles in Northern Ireland were in full flow and the IRA had carried out several terrorist bombings on the British mainland. There was a perception that the Government was looking impotent in the face of terror and that the Labour party was reluctant to go full throttle against the IRA because a lot of its core vote in the UK was from Irish migrants or people of Irish descent. This was not held out by reality, as Labour's Northern Ireland Secretary, Roy Mason, took a particularly hard line in tackling terrorism. Mrs Thatcher's statement that she would not negotiate with terrorists convinced a lot of people that the Conservatives would be uncompromising in tackling the IRA.
There was a perception that the Soviet Union was winning the Cold War, and this was amplified by pro-Conservative newspapers. They described with relish the terrifying new weapons that the Soviet Union was introducing, such as the Tupolev Tu22 Backfire supersonic bomber and the SS20 ballistic missile, both of which could hit London with little opposition, the Mil Mi24 Hind gunship helicopter and the Kirov-class battlecruiser that supposedly had the capacity to sink half of the Royal Navy. They also bulled up the disparity in size between British and Western armed forces and those of the Soviet Union and Warsaw Pact. They also claimed that the West had capitulated to the Soviet Union at the 1975 Helsinki Accords. The message being promoted was that Labour was weak on defence and that the Conservatives would be robust defenders of the UK.
There was the perception that the UK had become weak and was no longer standing up to aggressive adversaries across the world. The hiking of oil prices after the Yom Kippur War in 1973 and the arrival of wealthy Arabs in London during the 1970s gave the impression that they were top dogs now. This was amplified after Foreign Secretary David Owen apologised to Saudi Arabia after the screening of Death of a Princess on ITV. The apparent capitulation of the UK to Ugandan dictator Idi Amin in 1976 to secure the release of a British national who had been sentenced to death gave the impression of a country that no longer had the balls to defend itself internationally. Mrs Thatcher gave people the impression that the UK was no longer going to be pushed around.
Amongst older voters, there was the perception that the country had lost its moral compass following the advent of the permissive society in the 1960s. Remember that in 1979, most males in their 50s had military service during the Second World War. Mrs Thatcher was particularly friendly towards Mary Whitehouse and the Conservatives were able to exploit older voters disgust at the visible symbols of the permissive society i.e. rock music, long hair in men, sexual promiscuity and the numerous "liberation" movements that became prominent in the 1970s like women's liberation, gay liberation etc. Finally, at the end of the 1970s, punk rock appeared to be the final straw. Remember the furore about the Sex Pistols song, "God Save The Queen", which was released in Queen Elizabeth's Silver Jubilee year?
Finally, two events wile the election campaign was in progress may have helped wavering voters to make up their mind. One was the assassination of Airey Neave when his car was blown up by an IRA bomb in March 1979. The other was the Southall riot in April 1979 when activists from the Anti-Nazi League and the Socialist Workers Party tried to prevent the National Front from holding a meeting in Ealing Town Hall. I am sure that the Conservatives exploited both events to remind voters "this is what we are up against".
With no industrial unrest in the 1970s, I think the most likely outcomes would have been either a hung Parliament or a narrower win for the Conservatives. The Labour leadership looked exhausted and Mrs Thatcher had revived and energised the Conservative Party. The Winter of Discontent was a godsend for her but I think other factors described above would have worked for her.
