Well, change your routine so it involves learning.
Imagine someone asks you to deploy a new server for a project, and you know that in this company, this sort of tasks is done manually. You spend the next hour creating the virtual machine and installing and configuring the operating system. The next day, another person asks you to create another server. Day after day, you do it, and notice that you're not learning anything.
A different approach would be to automate the task. You do the manual deployment a few times, and then you learn about automatic provisioning and other stuff. Now, when someone asks you for a new server, instead of wasting an hour of your work, you barely run a command, and while the server is being created, you do something else.
This “something else” could be actually be making your users' lives better. For instance, why would you make them wait for one hour for a new server? You start researching about the subject, and you discover Docker, which seems promising. You try it, and find that it responds to the needs of 80% of your users—the remaining 20% still need a fully-featured VM.
And so, now that you implemented Docker, in most cases, the users can have their environment provisioned in seconds instead of an hour. They find it so great that you have more and more requests for provisioning new environments. That's boring! What if you could learn a bit of software development? In a matter of months, you can create basic intranet sites. They are not secure or particularly comfortable to use, but they do their job: instead of calling you by phone and asking to provision a new server, users may simply do a request through your site. They like it, and you have even more free time to do more great stuff.
The result? When the company eventually collapses (and it has much less risk to collapse, thanks to this great system administrator who automated everything and make the system tasks much less expensive than before!), you have a lot to tell to the potential employers. Not only do you know a lot of new technologies, but you can also tell them how you changed the sysadmin culture in your previous company and how you lowered system administration costs for the company.
“But wait!” you'll tell me, “How would I learn if I have no seniors to learn from in the first place?”—this is what most comments to the question are about.
Learning from peers who are more skilled than you is a great way to learn. Not the only one, indeed, but it's still important to do it. This doesn't mean those peers should be at your workplace.
There is Stack Exchange. Here, I came across much more talented people than in any workplace where I've been previously. And the good part is that Stack Exchange is not limited to software engineering, or servers administration, or security, or user experience. It's all those experts, together, in all those diverse fields, and that's just great!
Back to my Docker example. Imagine you search for your own how to reduce time spent provisioning new environments. You may find some techniques which reduce it from an hour to a few minutes, but if you're unlucky, you may miss the Docker option. However, if you ask on ServerFault how to solve the time problem you have, there are chances someone will suggest Docker as an alternative to your current approach.
There are meetups and conferences.
And blogs. Don't forget blogs. There are obviously skilled system administrators who love talking about the things they are doing. Learn from their experience.
As an example:
I started my career of software developer as a freelancer. While it's a good opportunity to learn stuff by discovering a lot of projects, it doesn't necessarily mean that the projects you work on will actually be worth discovering, nor that you'll meet talented people. Personally, I did, but not every project was really worth it.
In 2013, I was financially forced to spend a year in a company where there were no professional developers whatsoever. There were so-called coders who knew nothing about programming. Still, during this year, I learned a lot, both in terms of technologies and in terms of general software development skills, by participating on Stack Exchange, reading books and articles and going to conferences. The time I was spending in the company was a total waste of time; despite that, I learned a lot during the year.
In 2014, I joined a different company. While there were a few people more skilled than I, we never had an opportunity to talk much. Still, thanks to the books and to Stack Exchange, I learned a lot as well.
Now, I have a chance to work in a company where most people are more skilled than I. This is an excellent opportunity for me to learn from them; this doesn't mean I will stop reading books and participating on Stack Exchange.