Who cares? Iirc the Tories got approx 16% of the Holyrood vote, many of them are aging, some of them are going to disappear. Some of them might give up on voting, what's to say there won't be a Scottish Conservative party? They may well keep voting for them.
Where have all the English left wing voters gone?? Who do they have to vote for?? The SNP aren't going to have to court any extra votes imo, well they have to court mine coz I'm not a fan.
Who are all the Lib Dem voters going to vote for? There are more than 2 political parties in most European countries. Have you ever seen a German ballot paper? They're massive!
The SNP are not going to get overrun by Tories any time soon, but as to who they switch allegiance to, if they do at all, how the heck would I know? I have studied political figures for years and honestly the Tories ARE a dying bred in Scotland.