Air Carrier Captain reported while in cruise flight experiencing a right pack failure resulting in a rapid descent to 10;000 feet and the flight landed at their destination safely.

Narrative

During pairing Aircraft X on Day 0; after landing and taxiing in from flight XXXX ZZZ2 > ZZZ we received a R PACK AUTOFAIL caution message. We ran the QRH and called maintenance when at the gate. After consulting with dispatch; maintenance control and the bridge about options of repair; delays and getting a new plane the end result was a deferral of our right pack and continuing out for our next leg to ZZZ1.While enroute from ZZZ to ZZZ1 30 minutes out from destination at FL300 we received a CABIN ALT caution message. Cabin altitude was 8500 at the time. I; the captain was pilot flying. I called for my FO to run the QRH and took control of the radios. The FO ran the checklist for 'CABN ALT (Amber)' which did not resolve the issue. That checklist led to the 'Manual Pressurization Control Procedure' in the QRH. The FO did this procedure and it was not working either. Cabin altitude had now slowly risen to 8700. That was the end of all guidance in the QRH. I also ran the QRH myself checking the FO's work with the QRH and confirmed he did everything correctly.With neither checklist resolving our cabin altitude/pressurization issue; I made the decision to descend to 10;000 and advised ATC that we need a descent. They approved us to FL240 initially; we advised them of our pressurization issue; and then they cleared us down to 10;000. I did a very expedited descent in speed mode; power idle and full spoilers. During the descent to 10;000; after the QRH had been completed; the FO took the radios back and I continued as pilot flying. Shortly thereafter; not long into our descent; we received a 'SMOKE AFT LAV' Warning message. At that point the FO advised ATC. ATC responded asking us about souls on board; fuel remaining and intentions. We told ATC to stand by and I asked the FO to call the flight attendants to check on the status of the aft lav (Which is the first step of the QRH). During the time that it took for all of that to transpire the warning message cleared on its own before we were even able to run the QRH. He calls the flight attendants who confirm a female passenger was in the lav acting odd. The passenger denied smoking or vaping. The FA did not see or smell any sings of smoke or fire in the lav nor did they smell or see any tobacco or vape products. Based on this information and my past experience with this issue; I was convinced the brief warning message was due to that passenger vaping in the aft lav. I advised ATC of the developments and clarified that we had two separate issues; that we still need to descend to 10;000 for a pressurization issue but we no longer have a priority handling for smoke in the lav. ATC cancelled our priory handling at this time and we continued our descent down to 10;000.Somewhere around this point my FO offered to take the controls so I could better manage the situation which I thought was a good idea and accepted. FO is now PF and I am PM. Not sure exactly where this switch happened as there was a lot going on. Somewhere around FL230 we started to regain control of pressurization. I coordinated with dispatch confirming they still wanted us to continue to ZZZ1 which they confirmed saying as long as we had control of pressurization to continue which we did.We landed uneventfully in ZZZ2; taxi'd to the gate and I began speaking with dispatch; maintenance and the duty pilot for next steps.Suggestions: I would recommend reviewing the Manual Press Control Procedure in the QRH as guidance just ends assuming the procedure works. I would consider adding guidance for the scenario that it doesn't work. Also in the Cabin ALT QRH I could see someone accidentally selecting EMER DEPRESS to the on position and depressurizing the cabin unintentionally. Not sure how; but further clarification or warning of the selection of that switch position could be beneficial as the 'Confirm OFF' verbiage resembles how we verbalize confirmation of a guarded switch before pressing it during the competition of the QRH.