If the actual rules from the manga/anime were to be applied, then Mia's death would be certain once her name was written down in the notebook. Looking from the rules from the Death Note wiki,
- The human whose name is written in this note shall die.
- If the cause of death is written within the next 40 seconds of writing the person's name, it will happen.
- If the cause of death is not specified, the person will simply die of a heart attack.
- After writing the cause of death, details of the death should be written in the next 6 minutes and 40 seconds.
So, you can only add the causes and conditions of the death of the person. Essentially, this means you can alter the way a person dies, but not whether a person dies.
If the owner of the Death Note decides to write in a condition anyway, then one of two scenarios might happen:
- The condition is ignored entirely and the victim simply dies of a heart attack.
- If some part of the conditional clause may be used as a cause or condition for the death of the victim, then it will be applied (provided it is physically possible).
As an example, if Light wrote the following in his Death Note,
If she takes the book, she commits suicide by jumping out of the Ferris Wheel.
According to scenario 1, Mia Sutton dies to a heart attack. According to scenario 2, Mia Sutton dies by jumping out of the Ferris Wheel (which is physically possible, since she was in a Ferris Wheel in that scene). I'm not entirely sure which scenario will occur, but I personally lean towards the second one.
As a side note, I actually caught the exact wording Light used for Mia's Sutton. According to the transcript from the same website you posted,
Mia Sutton is killed when she accepts the Death Note from her
boyfriend. As the Northwest Ferris Wheel mysteriously collapses... she
pulls the page with my name on it from the note. And it is ultimately
consumed by fire. Although her boyfriend lands safely in the water... Mia strikes the shoreline... dying instantly.
Notice Light used the word "when" and not "if" in the conditions for Mia's death, which presumably means he had every intention to kill her. This suggests that the Netflix version also did not allow the use of conditional clauses regarding a person's death.