If you vomit in the first 90 minutes after swallowing Mifepristone, it may be less effective. However, as advised by Women Help Women, you can still continue with the abortion and take Misoprostol the next day.
If you vomit 90 minutes or more after swallowing Mifepristone, then it has already been absorbed and you do not need to worry.
Since Misoprostol is held under the tongue for 30 minutes and you do not have to swallow it, vomiting is less likely to be a problem. However, if you do vomit during those 30 minutes you should take another dose of Misoprostol. Putting Misoprostol inside the vagina is also an option.
Nausea is very common during the medical abortion process. You can take medicines like Motilium to help with this.