Just as a thought - maybe you could interpret it as there was no force play because he reached the base safely prior to the illegal slide (assuming he touched the base during the slide). Then the illegal slide doesn't fall under the "force play slide" rule, just a regular illegal slide. Maybe you could judge that the ss wasn't attempting a "force" play - just a "play" because he had no opportunity to get the force.
The rule itself doesn't require a follow on play, so I don't know if you want to factor that in? I'd have a hard time awarding a double play in the scenario you present - but the rule pretty much would call for it.
The rule would be better if the umpire was allowed to use judgement as to whether or not there was going to be a continuing play.