The only part that matters is arriving and paying, regardless of whether they dance together. My experience working for one place and being on the board of another is that no regular milonga (rather than a big ball, festival, marathon, or other special event) gets most or even very much of its earnings from strangers. They all depend on certain couples who have "their place" – and to a lesser extent, singles who turn up because they know their favorite partners will be there – week in, week out. The tourists, and even the odd dancer who crosses town to check out the weird place far from where they live, don't really do (pay) enough to keep such events alive.