The shift in theory back to Jon/Richie problems since Ava's video was posted makes sense, but I'm going to play devil's advocate here...
1. In 2007 Richie's stint in "rehab" was actually just a one week detox at a hospital in LA. The announcement of him not touring this leg was on April 2, a little over 3 weeks ago. He could have just entered the same type of 7 day detox program followed by therapy, which would explain him being around and available to drive Ava to school today.
2. We know from past history time off for Richie leads to trouble. When he entered rehab in 2011 it was at the end of a one month break from the road. April 2 of this year was the end of a 2 week break from the road. Not the month long bender requiring a 30 day rehab stint, but a couple of weeks hitting the bottle warranting a 7 day detox. At 1:15 he even admits being on the road isn't the problem, it's time off that is the problem.
3. The fact that Matt has insisted that the TMZ article is completely off with this one, explicitly said Jon and Richie are not fighting, said it's up to Richie to make an official statement and he "WILL be back on the road" squashes the whole gag order theory. I know Matt is theoretically a nobody, but he still works for the organization and cannot make statements like that (whether they be true or false) if there is some sort of
take our secrets to the grave clause. He would simply say "personal reasons" and leave it at that, not reassure his twitter followers that the fighting rumors are bullshit and that he'll be back for the European shows.
Again, the situation could very well be as Beaky has suggested, but I'm not so sure alcohol being the reason can be ruled out.