SCi Entertainment Group are the parent company of Eidos Interactive, and as such have ultimate control over games such as Tomb Raider. However, SCi have been in financial difficulties recently and have reviewed their business model. In cases like this there is always the chance that the parent company might sell off their more attractive assets to raise capital, but in a recent announcement (29 February 2008) SCi have confirmed that Tomb Raider is not in their sights and is safe for now! In fact SCi have stated in that press release that Tomb Raider is a prime asset and as such is one of the cornerstones of their business, so there's no reason to be concerned that it will be sold off.
The next game in the series, Tomb Raider: Underworld, had already been pushed back to Christmas 2008 on all platforms (that is, all platforms they develop for - that doesn't mean on the Mac...) That date has been confirmed in the above press release, so although not set in stone TR Underworld is looking good for next Christmas!
(If the link above to the SCi business review doesn't work for you, then go to this page and open the RNS press release dated 29 February 2008 and titled ')