Character mistake: In a scene when Watney is recording his video log, he imagines what would happen if his pressurized shelter suddenly would break. He concludes that he would implode, but the correct wording would be explode.
Character mistake: The flags (both USA and China) on Iris 2 when hung vertically, were hung incorrectly, and appeared as such on the cover of the "Times." They should have been "reversed" so that canton is still in the upper left hand corner. (01:30:35)
Character mistake: As Teddy is announcing the bad news, he calls Mark Watney 'Mark Watton'. (00:09:48)
Answer: The crew (and mission control) are in constant contact with the previously dropped MAV and would have aborted the mission and continued back to Earth had the MAV become inoperable before their arrival. Weir states this explicitly early in the book.
Answer: Yes, it is very risky unless the new Ares MAV is in an area with much calmer weather patterns.