For the first part of the question, this means that the experimental evidence is sufficient to rule out decay with a lifetime of up to the figure given of ~$10^{29}$ years (~$10^{36}$ s, or $10^{12}$ Ys), and is consistent with a lifetime even longer - including up to infinity. In particular, we have observed NO spontaneous decay whatsoever with our current instruments (such as Super Kamiokande, which is designed to look for this kind of thing)... but because we've only been observing so many protons for so long in them, we can't rule out that it may undergo a decay with a lifetime longer than this, that is, that none have been seen to decay so far, but that doesn't mean one won't be seen to decay in the future. And empirically, this is actually true of all particles - we can never prove a particle (or anything else, for that matter) to be absolutely stable since this would require observing it for an infinitely long period of time, which is impossible (if for no other reason than the Universe will cease to be able to support life due to increasing entropization via the second law of thermodynamics at some point in the distant future - that is, the dissipation and dispersal of all concentrated, available-to-do-work energy into dispersed, unavailable-to-do-work forms, and "work" includes "biological life processes" and "doing experiments", not just force over a distance. But even without that, there's just the simple fact we "won't reach infinity" - something that itself gives rise to interesting philosophical paradoxes if you imagine a state "when infinity has been reached" and how the being would have accounted for this when it couldn't have reached it before...). That is, it's even possible the electron could decay after some ungodly amount of time, and we will never be able to prove it otherwise, though the theory we have so far says it shouldn't.
Which of course makes one wonder then why we'd be looking at proton decay anyways, and the reason for this is some theories suggest that it could happen. None of them have any experimental evidence to back them up yet; these experiments are a way to try and find some (namely, if we observed a proton to decay it would be exactly that evidence we were looking for). In particular, so-called "grand unified theories" suggest that on a scale of $10^{32}$ years or so (so higher than the experimental bound so far) the proton will decay to a positron and a neutral pion ($\pi^0$), the latter of which would instantly decay to gamma ray photons, thus leaving only positrons and photons, and the positron may annihilate with an electron, the end result being the whole universe will eventually be degraded to a bath of photons alone (of incomprehensibly long wavelength due to cosmic expansion). This answers your other question. Now this is not the only possible avenue by which decay could happen - another possibility is decay through higher-order processes related to the gravitational interaction, in particular so-called "virtual black holes", which would (I believe) lead to the same decay result (a positron and pion) but with a much, much longer half-life, here $10^{200}$ years, making it intractable to test since you'd need to be observing around $10^{200}$ protons to see one decay, and there's only on the order of $10^{80}$ protons in the entire observable Universe, a full $10^{120}$ too few (to imagine this, imagine that all the observable Universe's worth of protons were inside a proton, and this proton was one in another observable Universe each of whose protons was a whole observable Universe of protons, and then imagine this Universe was a proton inside a planetoid-sized object of protons each of Universes of protons of protons of this type.).
Regarding your other question, the quarks on a proton have fractional charges where two have $+\frac{2}{3} e$ and one have $-\frac{1}{3} e$. So in theory you should be able to separate them with a field, BUT you cannot isolate quarks, and the reason for this is the strong force or color interaction between them fails to let go with distance and as a result you could pull them as far as you like and they'd still be attracting each other as madly as ever ... but as you do this eventually you build up so much potential energy you rip a new quark/antiquark pair out (you have put in enough energy doing work against the strong force that it equals the mass-energy of those particles and then quantum uncertainty puffs one out of the vacuum), and it "snaps" into diquark particles, so no lone quarks. (And according to @JEB, it might also be that the electric field breaks down the vacuum before you begin to significantly polarize the proton anyways so you can't even get that far.)
