My 04' SE just hit 270k miles. Over the past 7 years I've replaced basically everything but the engine and it's still running like new with no oil leaks, but it burns a qt of oil every 2 fills ups. Also, when I replaced the VC cover gaskets I reused the OG spark plug gaskets instead of just replacing the VCs (the gaskets are not serviceable) because I was dumb. No oil getting into the spark plug holes as far as I can tell so far but I assume it's just a matter of time. I occasionally get a P0420 code but I just reset it and it's good for a couple months (still has OG cats). It's my daily driver and I take it on surf/overlanding trips to Baja a few times a year 12 to 18 hours deep and with the high milage I'm concerned something will break in the middle of nowhere and I'll be f***. I take great care of my truck but how long do these engines last reasonably? Should I just make a preemptive strike and have a mechanic do an engine swap or a rebuild? What do you suggest?

I have read posts here touting well over 300K miles on their Pathfinder or QX4 and still going strong, with no oil having to be added or no more than a quart between oil changes. Those all had oil changes every 3K miles since the beginning of their long life. Mine has over 230K miles on it and burns less than a quart every 3K miles. Once the bearings and rings start burning oil like you are seeing, there is no stopping the ever progressive increase of oil consumption and inevitable wrecking of your cats and gummed up engine works. (e.g. intake and exhaust valves, piston rings, combustion chambers, VVT, PCV valve, intake manifold, etc.) Sludge build up is likely at this stage as well. At 270K miles, your Pathfinder has seen a reasonably long life. I don't have a crystal ball or any way to predict how much longer it can go. A preemptive move to replace or rebuild the engine , before it breaks down, is reasonable.