My very non-qualified thoughts about this, I'm definitely out of my depth here, but it's kind of fun to think about these things :)
Not releasing it as planned could very well be worse. It could easily be seen as an implicit acknowledgment that the plaintiff has legal standing, and that their claims have merit. This could then lead to a situation where an IPO would have to be delayed, potentially for years until it all has been played out in court.
I'm quite sure most potential investors will assume that this particular suit is likely to be timed based on rumors of the IPO to interfere maximally with it. Maybe in the hope of either a quick settlement or to effectively create an out-of-court punishment via lowered IPO valuation to deterr others from trying to manuever the legal terrain in a similar way as Spotify is claimed to do. Whether the plaintiff has standing or not.
Going forward without deviating from schedule, or even quicker than schedule, sends what is probably the strongest possible message that could be sent to bolster the IPO and minimise value loss. It says: "We're not afraid of this suit"
Risk estimates in preparation for an IPO regarding a company like Spotify almost certainly includes assesment of risks by various actors that might want a piece of the cake through legal action.