My first time saying this to the chat btw.
Which playable airport in your opinion is (almost) the most fitting to be strictly for dead airlines like Monarch, PLAY, etc. to enjoy their stays? Think about a Retirement Home International Airport-type of stuff. Still appreciate some ideas tho.
Monarch would definitely be INN as they flew there until their demise in 2017, sometimes having several aircraft on the ground at a time. Sadly the 757 isn’t available even though it was also a regular until 2015. Long haul for MON, none of their irl destinations exist for the A330 but BKK or MCT or even SAN and MSY would work, you’re looking for a charter holiday destination so those are likely the best bets, maybe GRU too. A300 was used on longer haul routes, irl used to use Bahrain for stopovers on its way to Goa so could be one for MCT but later in the types career it was used on short hops to the Canaries and Greece.
PLAY served PRG I believe as well as IAD.
Now off the top of my head remembering some more dead airlines, currently you have Thomas Cook, who only have the A330 and as per MON’s A330, has no irl destinations in-game but I’d say to give it the same treatment.
If you think of any others, happy to help 
Thomas Cook flew to BOS, JFK, SFO and LAX so using them at IAD and SAN isn’t too far off where they actually went. Really, we need the A321 or 757 to use at INN, currently the only place we have in game that they did fly to.
I don’t have a dedicated airport for dead airlines but instead throw a few in for variety at every airport. I typically choose historic airlines based on formerly flown routes and bases. For example:
INN — Monarch,
BRI — Alitalia
PRG — Play (I won’t put this in IAD as there isn’t an international terminal C gate in game unfortunately).
SXM — Thomas Cook (Thomas Cook Scandinavia, now Sunclass flew here in the mid 2010s, and we don’t have the TCS livery, so this is as close as I can get), JetAir Caribbean, Seaborne (now only does seaplane operations), Silver Airways
MSY — Spirit, Silver Airways (I also use the republic and mesa tails on some small plane routes here as variety and a nod to those airlines history)
ZRH (planned) — Braathens Regional (there’s a few images of their B463s here, and since Jumbolinos are so iconic at ZRH it’s a logical choice to me).
Hope that gives you some ideas!
Braathens I believe also did some runs into INN for a time when they transitioned across from being Malmo Aviation.
I have my B463 BRA contract there now actually, but I’ve decided I’ll can that contract at my INN once I get it at ZRH. The only evidence of them flying to INN that I can find would was before they rebranded from Malmö and we don’t have that livery in game unfortunately.
Yeah, thx for the ideas.
Maybe I’ll let the dead ones share PRG’s Terminal 2 and Stands 54-58, T6, and 60-65 with airlines from countries with no religion (CSA, KLM, Smartwings, and more) for that matter (also Stands 70-75 with Israeli airlines and my fleet).