I'm wondering if there will be an opportunity going forward to earn past event items again. 

Take for example those who bought the game after the Los Muertos event, will they have an opportunity to earn Catrina again this year when the Day of the Dead rolls around in November again this year? 

For the community event at Lunar New Year, as a community we did not earn enough points to unlock the persona. Will this persona be available again to potentially unlock in a similar event Lunar New Year event early 2023? 

Similarly to the Los Muertos event, will the Holi event come back next year with another opportunity to earn the same rewards, perhaps with different challenges or other new chapters that include a second set of event items? 

If these events become cyclical, then players always have something to look forward to - a new player can look forward to earning the past event items as well was whatever new was added, and current players can anticipate or even select which particular event gives them rewards they are more interested in (e.g., if they really like the design of the rewards for the Holi event then they can anticipate the Holi event and know when this will be to provide them with new items they actually want). In this system, nobody ever feels like all is lost when the event ends and the rewards are gone forever, as at the very most they will be back in 12 months time. It also helps to circumvent issues with bugs or difficult challenges because there will be another opportunity to earn them again. 

Having an event cycle is a compromise between having time-limited events, where they are only around for 3 weeks and have to get in quickly, and just putting challenges into the game to unlock at your leisure (i.e., have the Los Muertos challenges and Holi challenges in the game forever, and unlockable whenever you do it - like an achievement with rewards). While I for one would prefer if all challenges just accumulated in-game like this and I could let them build up and then play a few games to get all the rewards at once, I'd least like to be certain that the event will come back and the rewards can be achieved again if missed out at the time of the first event. 

Yep there will be more opportunities to get previous content from the events/challenges do not worry :) 
I can not tell you a specific day for it, but we will let you know in advance.