The chances that the top 2 GC riders would have the exact same time, after ~20 stages, is almost nil.
The chances that either GC contender could actually win a sprint finish by a big enough margin to change the GC is also zero. Even if they wanted to go at it, it would be pointless.
The only way the GC riders can duke it out in Paris is if the organizers make the last stage a time trial, like they did in 1989. But since a flat stage does not result in any GC changes in the modern era, functionally there's no difference between doing the ITT on the last day or on the 2nd-to-last stage. (I.e. this year got as down to the wire as it ever gets.)
The final stage is for the most part a parade, just enjoy it for what it is.