As an experience changing jobs to a higher position is a matter of courage ..Which I dont have now..So do it..
When a person becomes older also becomes lazy too..Like me 
You do get the 'comfy slippers' mentality.
Trouble is, been doing my current role for 7.5yrs and getting restless. A few technology changes keeps you on your toes, but a certain staleness working on the same site for that length of time...
Well I have been with the same company for 15 years, but I am needed if I left who would do my work?
Apart from a paper exercise change of employer about 3 or 4 yrs ago, I've been with same company for 19yrs.
And there is always someone who can do your job. Probably do it better as well. Nobody is irreplacable, no matter how much we like to think we aren't. It may take a replacement a week or 2 to get up to speed, but everybody can be replaced.
Hence, I would have no quilty feelings leaving my current role.
Thats true.. only replacing the programming projects and workers need a bit more time compared to IT administration..
And if they had the last version of codes 
Well I have written large chunks of the application. more of our DOS app than the Windows app, but it would take ages to understand the system to know where to do changes - eg new pricing systems ect
Well, heres the acid test to tell whether or not you're indispensible.
Think of a number that you'd like to get paid, in your wildest dreams, and then double it. Go to your boss in the morning and tell him that, unless he pays you that sum of money, you are going to leave and set up on your own. If he gives you the money, you are truly indispensible. Otherwise..........