As long as you can at least open them up to inspect them before you leave, and change them if you think there's a possibility they may fail during your journey.
I now trust the GXP BB a lot more than the old-fashioned type. The reason is that putting the bearings external like that gives room for more balls to share the load, and it also reduces the load on them because the two sides are farther apart. In fact, the right-side bearings are almost in the plane of the middle chainring. If you want to take an extra BB with you on an around-the-world trip though, it wouldn't take much room, as the spindle is part of the right crank arm, not the BB. Removing the crankset takes only an 8mm allan wrench, nothing else.
I worked in a bike shop in the 1970's when all wheel bearings were cup-and-cone. Although I saw a few that were pitted because they had been installed too tight, I never saw any that actually failed. I even opened one up that had been packed without any grease at all and ridden that way for a long time, and it looked perfect. When I opened my rear Shimano Ultegra hub up a couple of years ago to replace the failed freehub body after 8,000 miles, the grease was still that clear yellow-green color Shimano uses. No graying at all. When I opened up a Campy one after 20,000 miles and cleaned it up, I could hardly see where the bearings had ridden on the races. (I can't say the grease was clear, because it was black moly grease when I packed it.) I wouldn't have any qualms about beginning a 3,000-mile trip without re-packing or inspecting my hubs. I know they're fine. I would be more concerned about a freehub body going out again (although I munched freewheels too, and broken rear axles, something that doesn't happen with a freehub body).
All my bearings get cleaned, regreased (waterproof boat trailer wheel bearing grease, no less!) and adjusted at least every 2,500 miles, or whenever I think it might be necessary.
Do you do that with your car too?
And yeah, I meant cassette. Although mine consists of loose spacers and cogs, not a permanet prefabbed construct. All of which were hand picked by me to achieve the exact gearing pattern/spacing I wanted.
I do kind of miss the days when you could order a freewheel with exactly the number of teeth you wanted on each cog. Well, actually you still can, mostly, from loosescrews.com . But with nine or ten cogs on a cassette, the spacing is pretty doggone close, closer than I had with my optimum touring half-step setup with a 5-speed freewheel and triple where through the cruising range each gear was 11.8% higher than the last which is possible only with 13-16-20-25-31 and 30-42-47 (the chainrings can go up or down a bit, together, like 29-41-46, without ruining it, but not the cogs), omitting the combinations that give extreme chainlines. AFAIK, TA is the only crankset manufacturer left that allows you to have virtually any combination of chainrings you could want (although I understand some sizes are running out and will not be made again). The disadvantage with this is that the parts won't be mated, so shifting is not as quick. The bigger cog or chainring won't help the chain up from its smaller neighbor at the right place to make it mesh perfectly with the teeth. The modern system, when used as designed, makes for shifting that's instant in the back and almost instant (less than half a revolution) in the front.
