The largest immediate impact would be on Hess share price. Mostly likely, a significant share price correction in the negative direction because the failure to merge implies that Hess cannot be sold to another entity unless we sell Guyana to Exxon/CNOOC first.
You may want to be thinking strategically around that time frame: if you hold a lot of Hess stock, do you want to continue holding on to it and hoping for a conversion to CVX shares when the deal closes OR do you want to get out of Hess stock before it takes a dive (in case of no merger) and re-invest elsewhere? Also, if you're of the opinion that the merger won't happen, the time to buy Hess stock again may be right after that initial drop.......
Medium to long term is a bit harder to predict, but Hess is generating close to a $1B in revenue every quarter right now and that revenue will only go up as each Guyana FPSO comes online. That would imply farm in opportunities with other operators (GoM and worldwide) or actually purchasing a small operator with a ton of growth potential. Having said that, I don't foresee JH staying on as a CEO (the S-4 filing shows that he's been trying to sell Hess to Chevron for at least 3 years now), but I also don't foresee any layoffs at Hess, either. It does look like Hess would need all of its employees to continue pursuing future growth opportunities -- regardless of whether they occur organically (through exploration or farm-ins) or through M&A where Hess is actually the buyer.