There are too many variables in each person's decision to do this.
Are you early retirement (15/55) eligible or close to it? I'd wait if close and then retire. Pension is based on home country base, not including premium, so if the new domestic assignment with XOM is secure to 15/55, I'd wait. Resigning you would wait until 65 to get a small annuity. By retiring at 55 eligible for Lump Sum.
Taxes... Not as big an issue as you'd think. Deloitte's going to handle for 2 to 4 years regardless, as mentioned previously. If new company also uses Deloitte for Expats, no problems whatsoever.
Been where you are and made the tough decision both ways, from and back to XOM.