Sepinwall asked the producers this question a couple of weeks ago.
https://uproxx.com/sepinwall/the-ame...ew-spoilers/2/
"We base all of this loosely on how the KGB funded their illegals, although it wasn’t always completely consistent. But in general, our understanding is that illegals got money to get their businesses off the ground, but were then expected to be self-supporting, except for their operations, which were funded by the Centre. So Philip and Elizabeth would have been expected to keep the travel agency afloat, and support themselves through it. But the KGB would have paid for anything spy-related – any operations. None of this would have changed when Philip retired.
Philip and Elizabeth were able to run their travel agency and be spies all these years. They had to do both. It wasn’t easy. They didn’t get enough sleep! Although spying probably didn’t take up as much time as it looked like on the show — we televised the parts where they were busiest. They probably spent more time at the travel agency than they did spying. (For real illegals, this was even more true – the cover work to spying ratio was much more strongly weighted towards cover work.)
We can’t say for sure what would have happened if an illegals’ business were going under. If a one time infusion of cash would have saved it, it seems likely the KGB would have done so. It also seems likely that, human nature being what it is, some officers may have hidden the truth from their bosses back home. In one historical case, an illegal made a fortune from his business, and sent all the excess money back to Moscow."