I'm not sure what you mean by "in practice deontologist who do not care about the ends are nihilists".
Half-assed nihilist, anyone who doesn't care about the consequences of their actions out of some weak sense of philosophy sounds more like the kind of people who excuse their actions by claiming nihilism when they still care about the way they do things (I have a friend who could qualify).
However, deontologists do not think that we can make moral assessments about the ends. Morally, the ends are irrelevant, according to deontologists--even if certain ends produce favourable effects.
And so when means and ends conflict, which they do on a daily basis (For instance, treat a deadtalking rule loosely to help your mafia team? A relevant example from today), a deontologist chooses the morally favorable mean. The end may be totally irrelevant, that doesn't stop it from existing.
In my day to day life, I've found the right mean usually leads to favorable outcomes, while a utilitarian approach can be far more of a gamble (for instance, as a child lying to get out of trouble). As I grew older and more experienced, it became pretty obvious that desperate measures were just that, desperate, avoidable, and not an optimal long term strategy even if the moral returns were sometimes greater.
Take for instance a thought experiment of a slightly less comic book nature. You're a stage performer trying to raise money for a sick relative who needs an operation. You have a fairly mundane routine that you've practiced to perfection, and with ticket sales projections you should be able to able to cover the operation by the end of the month before your relative takes a turn for the worse. On the other hand, you have an untested death defying stunt that puts you and your partner in danger, and is strictly forbidden by your manager. This draws greater crowds, generating more money getting your relative their operation within a week. When all is said and done, you can say "man it's good to be a utilitarian. That was the most moral outcome one could ask for." But instead, your partner dies in the stunt, the show is ruined, no money, no operation. Listening to your manager would have been the right thing to do, not just because your actions were reckless, but because you would been able to afford the operation eventually anyway.
In short, if your actions are sound their outcomes will be consistently more favorable. Deontologists might say they don't care about the outcome, but if their means never had moral outcomes they probably weren't moral means to be begin with.