Well let's narrow it by saying she meets with an accident before becoming PM, say during the '79 election campaign. (And no, I don't wish Thatcher dead.) How might the election have gone and the rest of British politics in the '80s?
Well, that's a rather peculiar one. Obviously, if Mrs T dies around the time of the election, the Tories will be boosted by the sympathy factor; we can assume they win at least by as many seats as in OTL, probably more - Thatcher was not an electoral asset to the Tories at this point and more people favoured Callaghan personally.
As to who would take over - well, at this point it's almost certainly not going to be someone wholly sympathetic to her viewpoint. The only person who was as such in the shadow cabinet was called Keith Joseph. KJ might have a run for the leadership himself, but after his 'eugenics speech' he would almost certainly fail, even if he can gather the support for an actual run. The main candidate of the right would be Geoffrey Howe, who would have better prospects than Joseph but, being largely untested in office, would probably meet the same fate.
In all likelihood it would have been Willie Whitelaw or (if Whitelaw does not contest, which is quite possible) Jim Prior. So the party would be lead from the centre/left. This could have all sorts of consequences.
To what extent this would abort Thatcherism is mixed; some of what we associate with Thatcher was not neccessarily hers and would have been purused by probably any Tory government. For example, council house sales - fulfilling Anthony Eden's very One-Nation idea of a 'property owning Democracy' - was an idea which originated on the left of the party and which she was initially sceptical of. Privatisation would probably still go ahead, but it would only be tentative and incremental. Water, Telecoms, and the other utilities would very likely be still kept close to the bosom of the state.
The handling of the economy would certainly be different (Perhaps with Peter Walker as Chancellor) - it's unlikely that the austere monetarism of the 1979-1982 period would have been undertaken, so economically things would look more like the 1970's than what we associate with the 1980's - managable levels of unemployment, fluctuating inflation, a still significant manufacturing sector. You would not have bust but you would probably not have boom either.
Other things might go differently as well; most of the Tory Party was determined to pass trade union reform after the humiliation of the Heath government, but few had the total resolve of Thatcher and some sort of 'compromise' might be arrived at, or reform might be only incremental. The Unions would probably not be smashed politically as they were by the miners strike.
The Falklands too - would such a government be quite as intent on 'ramping down' the defence budget as OTL's was as part of it's policy of monetarist austerity, leading to the withdrawl of the relevant navy vessels before the invasion? Would it actually put more credance on the subtle hints Argentina was dropping? Butterflies could be significant here. The government would be more pro-European, in approach if not significantly in policy, and perhaps the main campaign cause for the excluded right-wing of the Tory party might remain Northern Irish Unionism rather longer than it did in OTL.
In terms of other parties, the effects are probably beyond estimation, but it seems likely that the SDP-Alliance would not be as significant as it was in OTL, riding as it did on the back of the extreme polarisation of the two main parties in this period; equally, Labour might not be as humiliated as it was at the 1983 election in OTL, and if that goes hand in hand with no miners strike, that could be a very significant check on reform. The tone of the Tories would be very different, and less confrontational, and those figures who we associate with Thatcher - Cecil Parkinson, Norman Tebbit, etc - would not be prominent players early on, if at all.
So politics would progress, but it would not be the total break with the past which we associate with this period in all parties and the economy, and it would still be recognisable as a post-war system in many respects.