Sure. Let's go one by one:
Withdraw of the Adjustment of Status o What would the process be for withdraw of Adjustment of Status o If a withdrawal of the Adjustment of Status is submitted, within how much time do I have to leave the US?
Your spouse would write a letter explaining that she would like to withdraw the I-130 and associated petitions and send it to the address that is on the I-797 receipts as well as copies of all those receipts. She doesn't have to state the reasons if she does not want to. She should sign it and maybe notarize it to lend it more legitimacy.
Annulment of marriage (or divorce) o Is an annulment of marriage possible? I’ve looked at the grounds for annulment and from my read, it doesn’t look possible, but could there be a way for annulment if both parties choose to annul? o If annulment isn’t possible, what would be the divorce process (especially in light of the petitioning that has been filed)
That really depends on the local rules. It isn't an immigration situation. Normally there has to be some fraud or something like that. If you cannot meet the qualifications for an annulment, I'm sure you could do a simplified divorce that could take just a few weeks to a few months depending on how busy the court is.
Other considerations o Would there be any future impediments to my travel to the US? (My career entails a lot of travel to various countries including the US. My home country citizenship allows for short term travel (~90days) to the US without a visa, would this be impacted?)
Unfortunately, there would be. Why? Because you had immigrant intent and that won't be dismissed so easily. They most likely would not let you use an ESTA again but would rather you apply for a B-2 tourist visa and prove to them that you do not have immigrant intent anymore.
I will provide you with two links that may be helpful. The first is to an article that will explain what they look for when issuing a non-immigrant visa like the B-2. The second is a list of things that can be presented to prove non-immigrant intent and the strong ties to the home country.
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