Some 63 percent of investors polled by Bernstein voiced concerns that Diess' surprise departure would weigh on stock performance, while 22 percent thought it could improve it.
VW plans to list the Porsche division in the fourth quarter.
Porsche may already have to go public at a steep discount if it decides to go ahead with the listing as economic obstacles mount, Reuters reported last week.
"Mr Blume will maintain his role as CEO including after a possible IPO," Volkswagen said on Monday in response to Reuters' questions.
Just days before his appointment was announced, Blume and other Porsche executives speaking at its capital markets day sold a possible listing of the sports car brand as a means to give it more independence and entrepreneurial freedom while raising funds for the group.
"Such a double mandate can only exist temporarily in an emergency situation -- it won't work in the long-term," said Ulrich Hocker of the German Association for the Protection of Securities (DSW), which represents retail investors.
Most investors do not at this stage expect a delay to the listing. Some, including car industry veteran Ferdinand Dudenhoeffer speculated that Porsche finance chief Lutz Meschke may eventually take over from Blume at the sports car brand.
VW has not outlined any succession planning for Blume at Porsche.
Volkswagen's share price has nearly halved since March 2021, underperforming a 17 percent drop in the STOXX Europe 600 Automobiles & Parts Inde over the same period.
The company answers to a complex web of investors. Its supervisory board comprises workers' representatives and regional government, and members of a holding company owned by the Porsche and Piech families that is staffed in part with Volkswagen executives.
Porsche's Meschke is on the board of the Porsche-Piech family's Porsche Automobil Holding, VW's top shareholder and owner of more than half its voting rights, while VW Chairman Hans Dieter Poetsch is its CEO.
Tensions over who pulls the strings in Wolfsburg have spelled the end of the road for several Volkswagen executives before Diess, with former CEO Bernd Pischetsrieder and former VW brand chief Wolfgang Bernhard forced out of their jobs in the late 2000s after repeated clashes with the works council.
While Diess is largely given credit for Volkswagen's pivot to electrification -- lifting the carmaker from the reputational ruin of the diesel scandal to leading Europe's electric car market-- the governance issues caused by his confrontational approach to leadership ultimately weighed on the investment case, analysts at Stifel Europe Equity Research said.
"Poor corporate governance makes many investors shy away," Janne Werning, who heads ESG Capital Markets & Stewardship at Union Investment, a top-10 shareholder in Volkswagen, said at the carmaker's annual meeting last year. Union Investment, which repeated its criticism of VW's governance at the most recent annual meeting in May, declined to comment for this article.
