No, they won't.
The ETH in the pledge cannot be withdrawn immediately after the Ethereum merger. This is to keep things as simple as possible, after all this is the biggest and most complex upgrade Ethereum has ever experienced in the industry.
The ETH in the withdrawal pledge is expected to be unlocked within 6-12 months of the merger.
Off-Chain Vote
Timeline
Aug 22, 2022Proposal created
Aug 22, 2022Proposal vote started
Sep 01, 2022Proposal vote ended
Dec 12, 2024Proposal updated