I agree with the others. The actual relationship itself is just as meaningful and significant as one based on anything else, be it another fetish, a common interest, love, lust....

What's important is that a relationship evolves from just one base to as much as possible, I would find it hard to stay with someone who's a polar opposite to me in everything apart from one common factor.

So to answer your question - I would say that intensity varies between relationships, and a poor bdsm based relationship will be far easier to get over than a strong friendship based relationship. Likewise, a mindblowing bdsm is harder than a weak friendship relationship. It's about the quality, not the contents.