What happens if the primary EB-5 applicant passes away before the EB-5 process is completed?

In situation where the primary applicant dies, the remaining accompanying family members generally are not afforded the opportunity to enter the U.S. by themselves. In your circumstance, consider withdrawing the petition and re-file it with your mother as the primary applicant. Advisably, consult an EB-5 attorney on your options.

No, since after I-526 is approved, your father will still have to be the primary beneficiary for being eligible to file for the immigrant visa, and if he is deceased at that time, you would not be able to proceed. Best option may be to try withdraw the petition and investment, then refile having your mother as the investor.

If the petitioner dies, the petition is automatically revoked unless you can show the immediate family derivatives. That is, spouse and/or minor children are residents in the U.S. Residents here can mean present on a student visa or other category. Under section 204 (L), one can apply to reinstate the petition if one family member is a resident according to the USCIS definition.

You have not indicated whether you are currently living in Vietnam. If that is the case it might be difficult if your father passes before you all can get your conditional green cards. However, if when your father passes you were living in the United States and continue to reside in the U.S. on the date of the decision on the pending petition or application you might have some basis to continue with the process even if your father passes before his I-526 petition is approved. According to the Policy Manual 602-0017 published on December 16, 2010, for many years, USCIS had taken the position that the law did not permit the beneficiary of a visa petition to obtain approval of the petition if the petitioner died while the petition remained pending. New section 204(l) of the Act changes this governing law concerning an alien who is seeking an immigration benefit through a deceased "qualifying relative." Section 204(l) permits the approval of a visa petition or refugee/asylee relative petition, as well as any adjustment application and related application if the alien seeking the benefit in addition to the residency requirements is any derivative beneficiary of a pending or approved employment-based visa petition. From the list of aliens to whom the new section 204(l) applies, however, USCIS infers that "qualifying relative" means an individual who, immediately before death, was the principal beneficiary in an employment-based visa petition case under section 203(b) of the Act such as your father. That said, under 8 C.F.R. 216.6(a)(6), the derivative beneficiaries meaning you and your mother must still file, two years after you obtain conditional residency, a Form I-829 and show that the requirements for removal of the conditions have been met. As you can see, the rules and regulations are quite complicated here. You are well-advised to work with an experienced immigration attorney to check all the above facts and see if they apply to your case.

Consult an experienced immigration attorney to go over all options.

Unlikely to work.

There are certain residency requirements you or your mother have to meet. If the principal applicant is deceased, as long as the dependent family member resided in the United States at the time when the principal applicant became deceased, and continues to reside in the United States, dependent family members of I-526 petition are eligible to have the pending I-526 adjudicated.

Unfortunately not. I recommend you discuss with your attorney and consider all options.