Go dtí mo lá deireanach, 'til my last day
There are more some traditional phrases commonly used (in Irish) that are along the same lines...
Go lá mo bháis, 'til my dying day (lit. until the day of my death)
Go dté mé i gcré, 'til my dying day, (lit. until go in clay, earth)
Depending on your context, my own favourites would be traditional sayings...
Go dté mé sa gcré, 'til my dying day, (lit. until I'm in the clay, until I'm in the ground)
Go deo na ndeor.
I like the sound of the first one (go dté mé sa gcré) because of the combination of dté, mé and gcré (sa gcré may also be written sa chré, dependning on dialect).
The second (go deo na ndeor) is hard to translate literally into English. It would be equivalent to the English for all eternity, to the end of time, for ever and ever, etc.