Right, there will always be custodians. The point is it is a service not a requirement. Right now you cannot self custody cash at your house and spend that cash electronically with a card without being an accredited bank. With Bitcoin you can. But that same custodial service exists in Bitcoin. It just carries the same risk as a bank. Most people will trust a custodian and risk their asset for the privilege of not having to learn about wallet software and seed phrases. 

 Does Bitcoin become captured if there are no unilateral exits once you have enough sats to pay fees? 

 Define some terms for me, please. What does "Exits" mean in this context?
And to which fees are you referring? 

 "Exit" means making a transaction on chain. Satisfying a script condition for a valid transaction per consensus rules.

Sats/vbyte. Transaction weight fees.  

 So is the question is: is Bitcoin captured if you can make a transaction? 

I would say no but of course captured by what? The miners including your transaction in a block? The node runners validating? The entity sending the coins?