How do I return to my H-1B application if my I-829, Petition by Entrepreneur to Remove Conditions on Permanent Resident Status is denied?

Since you will no longer have a qualifying event to be able to extend your H-1B beyond 6 years (i.e. a pending or approved I-140, and no adjudication of I-485), I doubt you can transfer back to H-1B status without being cap-subject.

Regarding the ability to return to H-1B visa status, it is not clear why you were not able to qualify separate and apart based upon your approved I-140 petition unless the backlog under the quota was such that it still takes a much longer time. What you need to do is maintain your current H-1B status given the fact that it can take a year or longer to obtain the approval of the EB-5 Regional Center I-526 petition before you are eligible to apply for your immigrant visa or Adjustment of Status once there are visa numbers available. Generally speaking, visa numbers are available except for individuals born in China. Thus, I would continue extending your H-1B status and keep your current employment based upon your approve I-140 petition until you are eligible to apply for Adjustment of Status.

You may not return to H1B without first going out of the country for at least 1 year and then starting the H1B process all over again. You will be subjected to the cap, as you have already used the 6-year H1B period.

You have to re-apply for an H-1B but, since you will have been counted against the cap within the previous six years, you should be fine. However, you would still need to consular process.

You may not be able to transfer back to your H-1B status if you switch to a conditional permanent resident status for a host of reasons. First, the time between when you switch from H-1B to conditional permanent resident status and the time in which your I-829 is rejected will be almost 3 years. Second, the general rule governing H-1B is that it will lapse if you do not use it with any employer and, in your case, the lapse is likely to be about over 3 years. Thus, in this scenario, it is likely to be impossible to switch back to an unused and possibly lapsed H-1B after over 3 years. You may be able to re-apply and go back to the H-1B, but you will be subject to the existing rules as a new beneficiary and will need an employer to sponsor. Advisably, consult an immigration to consider all your options.

You do not have to do anything, as you will remain in H-1B status until your EB-5 is approved and you adjust your status to Permanent Resident.

If your EB-2 remains backlogged, this will likely be a basis to extend your H-1B, regardless of the EB-5 petition. That is, if your I-829 is denied, you should be able to revert back to your H-1B status provided the EB-2 remains backlogged.