I know a couple US domestic team directors (one current, one former) and one Euro lower-level ex-pro.

With the bikes the US teams I know kept the bikes. The rider could buy them at season end, at a ridiculously low price (I was offered a chance at some of the bikes, like $400 or $500), but the reality is that these bikes were used pretty hard. I think they priced it as "frame + components, wheels", meaning you could get wheels, frame+components, or both. With that team if there was a significant sponsor change then the spare stuff went out the door quickly. So, for example, when they no longer needed the forks they'd used for a year, the director got rid of them. I helped the team with some minor stuff and he gave me a fork as thanks (as well as a bunch of other stuff, all from the prior season). This is the team that offered me team bikes.

The former director ran a team that rode really nice bikes and he still had one a few years later. The team folded due to lack of money and the director was left holding the (really big) bag. Selling off the bikes helped cover that hole. We're talking quite a bit of money. I was shocked that, first, he ended up responsible for the shortfall, and second, that he made up for it selling a bunch of bike stuff.

The ex-pro I know put together some random bike he got through friends in the bike world. It's nothing special, an off brand frame with some I don't know components on it. No fancy wheels. He's still technically a Cat 1 and did a Pro-1 race a number of years ago, made it 48 of the 50 miles, and he was realistically 80 lbs heavier than he was as a pro. He still has an incredible engine. In the old days he had some incredible bikes but they were owned by the team. He also broke them pretty regularly, 2-3 frames a year, so he really didn't want the frames. He'd get a contract for the next year so he didn't buy/keep any of his bikes. Only when the contract stuff slowed down did he keep a bike or two.

The ex-pro and the one team that offered me a bike, they had racing and training bikes. The training bikes were the ones at home, they almost always had lower level components on it. When the ex-pro raced Shimano his training bike had Ultegra. The team at the time used Campy and their training bikes were either Athena or Chorus, I can't remember. Only the race bikes were Record. Training bikes also got regular wheels, like non-aero aluminum, for the teams and riders I knew.

As far as pros go some riders did it for reasons other than riding. One rider I know turned pro for a tiny team and said that he'd quit riding 100% after his cycling career ended. He really didn't like riding the bike and for the life of me I have no idea how he motivated himself to train. Apparently he's completely out of the biz now.