"Berlusconi is still extremely powerful, although that power is declining," James Walston, a professor at the American University in Rome, said this week.
"He still has enormous resources, he still has his media, he still has lots of very diehard supporters inside and outside parliament."
But he added Berlusconi would be "liable for arrest".
Walston said Berlusconi was particularly worried about a case in Naples yet to go to trial in which he is accused of bribing a leftist senator to join his party and undermine a previous centre-left government.
"There is a possibility, but it's unlikely, that the Naples judges will actually put him inside," he said.
He added that the same remote chance existed for accusations that Berlusconi paid off young women who took part in raunchy parties at his villa in exchange for favourable testimony at one of his trials.
"The immunity he has as a lawmaker is not complete but it offers safeguards against arrest. He will no longer have that from Wednesday evening," Walston said.
"If he is arrested, there would be mayhem," he said, adding that the move could have the effect of increasing his popularity and earning "sympathy votes".
"I think there are political considerations that the judges will make about the consequences."
Berlusconi is set to be expelled from parliament following his conviction for tax fraud earlier this year under a new law aimed at boosting public support for the legislature by getting rid of criminals.
The three-time former premier would also be banned from being a candidate in the next general election and faces the prospect of a year's community service as part of his punishment, but that is only due to be implemented from early 2014.
Expulsion from the Senate would mean Berlusconi being forced out of parliament for the first time since he was elected in 1994 when the media magnate entered politics.
Berlusconi on Monday appealed to fellow senators not to vote against him, saying that democracy itself was at stake and claiming that new testimony gave sufficient grounds for a judicial review of his tax fraud case.
But Walston said the vote on Wednesday was "highly likely" to go ahead despite delaying tactics by Berlusconi's "diehard" supporters in parliament.
"If the vote goes ahead, then he will be expelled."
Prime Minister Enrico Letta's left-right coalition is expected to survive the vote even after Berlusconi and his loyalists move into opposition to a government in which they are at least formally coalition partners.
Deputy Prime Minister Angelino Alfano, a former Berlusconi protege, broke away from his mentor and has said he and his supporters will stay in the coalition even if Wednesday's vote goes against Berlusconi.
"In the short-term it will strengthen Letta's government but in the medium term it will probably weaken him," Walston said, explaining that divisions in the centre-right and centre-left undermined stability.
"There are problems for the government on all sides."
Walston said Berlusconi had been "careful" in his 20 years in politics about not allowing any potential successors to rise through the ranks, leaving the party "very weak" if and when he leaves the political scene.