Zip - in a word. The Tories were an unforgiving lot. In Oct. '74, Heath conceded a defeat of a Labour majority of three. If Thatcher did worse, she would not have lasted five minutes.
Nah - that was Heath's third loss in four attempts.
In his first shot in 1966, he was facing a Labour majority of about 1 and lost to a near-landslide of a abour majority of 97.
He still had a second shot in 1970 (winning), and a fourth shot after losing the unnecessary election he called in Feb 74.
It was an effectively hung Parliament when the election was called in 1979 (and would have been in 1978 as well), so with Heath's precedent, she
should have had a second shot anyway (albeit her position was possibly more frail than Heath's in '66). The tradition of stepping down when you lose one election really only took root in 1997 - and even in 2001, Hague would have continues if he'd
made some progress beyond "moribund". Even getting somewhere short of Foot-esque levels of seats would have kept him in.
That said, the sexism of the time was notable. As long as Thatcher didn't suffer a landslide against, she'd have probably had a second shot.