I not a tiler and there's much more experienced people around here, but I have recently gutted and refitted a bathroom and can at least offer some advice.
I think that removing the sink is the easiest (and quickest) option, as cutting through tiles that are fixed to a wall is near impossible, and you're likely to damage the surface behind (e.g. plasterboard) when attempting it, and therefore turning this into a much bigger job than it should be.
From my (admittedly limited) experience, if the confidence is there to tile then there's more than enough to take a sink off. Most are just held on through a combination of fixing bolts (underneath where the soap sits), possibly additional screws and the taps. If you have isolation valves fitted to H+C pipes all the better, if not ensure that water is not running when both taps are open (either from mains or tank). If you don't have valves fitted then this could be a good opportunity to fit them (if wishing to change the tap in the future etc), but will involve cutting the pipe and remeasuring to ensure that the taps are still at the correct height and sit on the sink. To make your life easier, I'd remove the sink and then re-fit the taps back onto the exposed pipes, as this way you can then take the time with the tiling / grouting, as you'll be able to turn the household water back on without flooding.