DistroKid collects royalties & pays out monthly. I also founded AdBrite which paid out several million dollars per month, if that adds to DistroKid's credibility.
And the good thing is that even if your distributor disappears, your music is still in the stores. It's decoupled from the distributor. Tho I'm not sure how you'd manage your music if your distributor went away, but I'm sure there's a way. Also, the stores vetted DistroKid somewhat. Likely so they can avoid having to figure this out.