Removal of the president under the 25th Amendment requires a 2/3 majority vote in both the Senate and the House.
That is a tall order. A lot of Democrats would cling to a Biden sinking ship rather than admit the truth.
If that action were to fail, we would have a U.S. president with absolutely no confidence, from anywhere, in his mental condition, who continues as a babbling idiot - president.
Just to be precise, the 25th Amendment does not provide for “removing” the President. It only provides for the temporary transfer of the powers and duties of the President to the Vice President. Biden could reclaim those powers and duties by simply writing a letter to the Congressional leaders asserting that he is, in fact, able to discharge his office. The VP and Cabinet could disagree again, and the decision would then devolve upon the Congress. But in all cases, Biden would still be President, although, perhaps, in name only.