The first thing you need to determine is whether he's going to learn of their betrayal before it takes place, or after.

If he trusts the players to actually do their job, then he won't be scrying at them and placing all sorts of divinations on them to monitor their actions. I don't know what edition you're playing, but scrying can be detected by certain means, and if they feel that their employer is keeping tabs on them, the players may feel that the Wizard is hiding things from them, or that he has other plans for them once they locate the artifact.

Then again, if he doesn't trust them, then obviously he would track them. Perhaps fearful that they'll sell the artifact to a higher bidding competitor or something.

Anyway, if he learns of it beforehand, there are plenty of things he can do to prevent the players from achieving their ends without having to get up and go after them. It's always worth remembering that if the amount of effort that he expends in hunting down the players exceeds the amount of effort it would have taken him to obtain the artifact in the first place, then why hire the players at all?

Now, if he has some blood from one of the players, that's obviously a good excuse to lay a curse on that player - but not the others. Always ensure that the players' actions determine the consequences, so if one of the players was careless enough to leave some of his blood in the hands of a Wizard they intended to betray, I really would feel no pity in having nasty things happen to him. So yes, I do approve of the curse idea.

Other things he could do are hire another group of mercenaries/adventurers to retrieve the artifact before the players, or provide false information (via Sending or the like) to the players that would delay their retrieval of the artifact or endanger their lives, or just outright threaten them with all the horrible things high level wizards can do to nasty little treacherous mercenaries.

Or he could go to them and place them under a geas spell, as has been suggested, but players generally do not enjoy not being allowed to control their own actions.

Now, if he only learns of it after the players have successfully destroyed or hidden the artifact, then it really depends on how vengeful the Wizard is, or how much he cares about his reputation and fears that news of such an incident might endanger it or embolden his rivals.

Obviously they won't get paid if they don't do their job. So he might simply rant at them and ensure they never get another job in this plane again, forcing the players to only deal with the untrustworthy sorts who will betray the, therefore retroactively justifying the players' suspicions.

Or again, he could lay down a curse on the player whose blood he possesses. He could put a bounty on their head, or send some magical servants - Conjurations, Golems, Undead, depending on his preference or specialisation - to kill the players.