Since April, I've been at my current job with a midsize company (I have almost 10 yrs experience in total before this job - stayed 4 and 5+ years in previous companies). My coworker, who has been with the company for about a year, just resigned on Friday. We are the only two people in the company who have our specific skillset that we were hired for. Our skillset is not actually that rare in my experience, but by the admission of my boss and my boss's boss, the company has a lot of difficulty attracting qualified candidates and retaining employees. (I can tell.)
When my coworker resigned, our boss panicked and called us both into a meeting where we went over everything that had to be transitioned from my coworker to me. After this, my boss had a meeting with just me where I was praised repeatedly and was told that I was "appreciated" and that the company had a hard time hiring people like me (which I already knew per above). It sounded like my boss was scared I'd also quit (I've been looking, which my boss does not know, but the perception is correct).
I have only been at the company for about 7 months, so I don't have a huge amount of accomplishments. I have had good reviews so far and I receive praise from my boss and my boss's boss. I'm certainly in good standing - or slightly above good standing - but I'm not an outstanding performer.
Once my coworker departs (after the notice period), I would like to negotiate a raise. This will also coincide with my year-end review in mid-December.
When negotiating a raise, you need a list of your accomplishments so you can explain why you are worth more to the company. I will put together a list, but the real reason I'm worth more to the company is that I will soon be the only person with my skillset at the company (and the company has difficulty hiring replacements (on top of existing vacancies that go unfilled for 1-2 years (you read that right))).
This is different from the typical situation of asking for a raise because the primary reason my value has increased is that my coworker has resigned.
With that in mind, how can I leverage my coworker's departure into a raise?