Some people came back, i see new active people between level 26 and 30. I talked to some of them, many came back after a long break. The hardcore players are still active. So there are good chances to get raids done.
The raids are awesome, you meet new people but you also keep running into the same people. I also like how you can collect badges for the different gyms, it really encourages you to explore.
Gyms eventually get defeated and switch owners, sometimes they stand for a week, but it is not bad, if you have some time you can visit gyms and will find ways to get some pokemon into gyms, some stay 9 hours and then get kicked out (full 50 gold, ideal), some stay for longer, up to a week, and some get bashed too often.
When i have time and go out to play i sometimes get up to 8 pokemon into gyms. The ones that get bashed out too fast are rather useless. I like the ones who last 9+ hours, into the next day, or longer. When i have no time to play, ideally i still have one with 50 gold return per day.