Yeah, clearly the notion of "Perpetual Succession" cannot mean that there will be an actual Pope at all times and every moment in history. That's the key to understanding what it actually DOES mean.
Also, if there's a time limit for an interregnum that would somehow disrupt this perpetual succession, please let us know what that time limit is. 3 years? 5? 7? 12? 15? 20 years 6 months 3 days 4 hours 15 minutes 25 seconds? So the maximum time for a lapse cannot be defined quantitatively, as coming up with an arbitrary limit would be absurd. It must therefore be understood qualitatively.
Now, one can debate what that means, and when the papal succession would have been disrupted/terminated in principle ... but this can be debated and it not entirely clear.
R&R like to throw out "60 years is absurd." Then please do tell us the exact limit, down to the second. I find it "absurd" that for >60 years we've had a hierarchy that can't be recognized as Catholic and from whom we must break to keep the faith and whose Magisterium and Mass we need to reject, etc.