I'm one of only two people currently in a particular position in my company. We are the only people in the company with the skillset to fill this position. The position is an important one - I won't exaggerate by saying anything like "the place would fall apart without us" but it's probably fair to say that both of us leaving would have an immediate and noticeable impact on the operations of the company as a whole. The other guy has announced today that he'll leave at the end of September. I'm currently interviewing for new positions and I'm deep into the interview process with one company.
If both of us left the company at roughly the same time then I believe it would create a difficult situation for the company. We have a fairly large codebase + cloud infrastructure and so even if they could hire a replacement quickly it would probably take some time for a replacement to get to grips with everything. On a personal level I've consistently received strong performance evaluations and have been told many times that I'm valued by senior people in the company.
As far as I see, this is a prime opportunity to negotiate a stronger position and/or salary as I think the company would be very reluctant to let me go at the same time as the one other person fulfilling my role.
However, I don't imagine that explicitly saying "Jeff is leaving, give me more money or I'm out too" is going to reflect well on me. Instead I'd like to communicate the ways in which my value has increased with my colleague leaving and make it clear that I'd like to see an improvement in my own position if I'm to stay.
I should be clear that while I'm looking at opportunities in other companies, my strong preference for a variety of reasons would be to stay at my current company with an improved position. I'd only like to move if it's clear that there's no opportunity for progression in my current company.
What are some strategies that I might use in order to accomplish this?