Long term it isn't likely to be a big drop for four reasons:
1) This isn't some kind of negligence on their part. This is a completely unforeseen consequence of speculative execution. That is a technology, widely used, that has been around for decades. It isn't like this was something they were ignoring, this is something security researchers only recently figured out. So while they will get sued, since everyone sues over everything these days, it isn't that likely to succeed.
2) This is not an Intel only problem. Despite early reports, this is something that affects basically all modern chips. The Specter attack (reading in-process memory) is something that is probable to work on every processor. That it hasn't been demonstrated yet on every CPU is a matter of what the researchers focused on, not that the others are invulnerable. It'll happen in time. MalwareJake is pretty confident this is only the beginning.
3) The performance impact is not near the big deal it was made out to be. On normal systems, it is tiny if even present. Even on big I/O systems, it doesn't seem to be as bad as first made out. So while there is lots of nerd rage, it is hard to legitimately get that mad about it. Couple that with the fact that Intel never made any specific performance claims on their CPUs guaranteeing a level of performance.
4) It isn't that big a security hole. It is not the cataclysmic event that some people were (and still are) making it out to be. It is a covert data ex-filtration channel. That sucks, but we have been dealing with that in security forever, and they don't go away. You just have to work to make them difficult to use and to monitor for it happening.
So while it will cost them some money, it isn't likely to be an amount such as to hurt stock price.