When I say the Merlin has the votes he can do anything, he might get a vote to strip Eb of the Position of the Blackstaff, for refusing to take on Harry, and seek to award it to some favourite to take on Harry as a power up. Internal politics.
Now how much the Merlin knows about the Blackstaff and it origin is moot, as the Blackstaff seem to have generally passed on the Blackstaff to their chosen successor. Everyone out of the line of succession may know very little other than what it does. He may not know that it is an object of Winter, and that it may be ineffective against the Winter Knight (Eb didn’t draw upon it in his battle with Harry) and indeed any attempt to use it against an official of Winter may result in the Blackstaff returning to Winter i.e. Harry. Worse it might result in an insult against Winter by the White Council and specifically the Merlin. Eb probably knows this, Harry has (along with the reader) deduced much of this. Does the Merlin know?
A sick and crippled Eb, being pressurised to give up the Blackstaff might just do so, if it puts the Merlin in Mab’s crosshairs. The Merlin could not only lose the Blackstaff from the White Council, he could be facing a personal magical duel from Mab’s champion, who I believe is currently is Harry, now armed with the Blackstaff. Harry would be seeking to rescue his grandfather, humiliating the Merlin would just be a side effect. I do not think would kill the Merlin even in a duel, I do think he would force the Merlin to swear on his power so many times that should he break his multiple oaths he would rapidly become almost powerless, publicly and irrevocably breaking the Merlin’s power. The Saruman option. But beware Saruman had one last act of spite.
The Gatekeeper has stated that Harry would take on the White Council after challenging them in Turn Coat, saying that it wasn’t time yet. I believe we might be approaching that time, these events or something similar will force the issue. Mab does not care about an insult against Harry such as the boom in Little Things ( a Merlin plot I think) but an insult against Winter is a different matter.