The chances of him cancelling are not 50% yet, but in my honest opinion, they are most probably approaching the 50% mark.
I base my estimate on the following developments, in descending order of importance (to the Prime Minister):
40 democrats are expected to skip his speech
Biden has just announced that he won’t attend his speech.
Obama won’t meet with him.
Now you may say that Netanyahu does not care much about what the Democrats think.
But AIPAC does, and it has to work with them.
And should the current trend of opposition to Netanyahu’s speech at the Congress continue, its very possible that the Prime Minister’s office will get a warning from AIPAC. Something like “if Prime Minister Netanyahu does go ahead with this speech, he will be disrupting our work and making our job of garnering support for Israel unjustifiably more difficult. The cost of his Congress speech vs postponing it are far higher for us and for Israel’s position in bipartisan US politics. “
AIPAC is an organization whose advice ALL Israeli Prime Ministers take seriously, including Netanyahu.
So don’t dismiss the possibility of Netanyahu actually cancelling his upcoming speech in front of the Congress.