Stakers (or “liquidity providers”) can withdraw their liquidity (including the accumulated fees) by selling the Relay Token on Bancor or via a third party.
The amount they receive will be their proportion of the value of the Relay’s liquidity at the time of selling plus the fees accumulated in the Relay. Therefore, the staker may receive more or less than the amount they initially contributed.
See user guide on buying Relay Tokens here; selling follows the same steps: https://support.bancor.network/hc/en-us/articles/360031705151