Excluding Hollyoaks, the other three evening soaps consistently make up the ratings top 10's for BBC1 and ITV every week. The only shows to beat them are the likes of yearly event series like SCD, X Factor, The Voice, The Apprentice and I'm A Celebrity and these only run for a limited period each year. Unless the channels find other regular series that will pull in higher ratings than the soaps then the soaps are here to stay.
Hollyoaks doesn't figure in Channel 4's top 10 ratings often so it's possible that it could go in the next ten years but they may make their money back from tie ins, sponsorship and reruns on E4 so I wouldn't be too sure. The only other reason I could see any of the other soaps being dropped without being overtaken in ratings by another show, would be if ratings for all programmes on all stations dropped to figures that were so low that it was no longer cost effective to produce the soaps but I'd imagine they would pare down production costs as much as they could before they would let this happen (much like we've seen with the American daytime soaps being cancelled over costs and those that remain on air dropping big name cast members in order to save on salaries).