The mortgage is paid. The line of credit is sitting there at zero, and the payment you've been sending for years is now just cash in your account every month.
That last part is the dangerous part. A freed-up payment doesn't feel like income, it feels like breathing room, and breathing room gets absorbed. Six months from now the number is gone and you won't be able to name what it bought. The households that keep the gain are the ones that assigned it a job in the first thirty days, before anything else got a vote.
So assign it. The line stays open, and it stops being a mortgage tool and becomes two other things. First, it's your standing liquidity, which means you can hold less dead cash in a savings account and still sleep, because there's a committed source of funds you can draw in a day. Second, it's the funding runway for whatever the next asset is.
That's usually where the policy comes in. The mortgage payment you just retired is, for a lot of people, roughly the size of a well-designed premium. Redirecting it does two things at once: it builds a hub you own instead of one a bank can close, and it puts a death benefit over the house you just paid off. If that's the direction you're headed, the funding question is laid out at how much to actually put into a policy.
Keep the line active, though. Lenders close HELOCs for inactivity, and an unused line with no draws for a couple of years is a candidate. Run something small through it once or twice a year and pay it off. Same reason you keep an old credit card open.
And keep doing the monthly review. Ten minutes, once a month, and it catches spending creep while it's still small enough to reverse. Skip it for a year and the freed-up payment is gone into the general noise of your life, which is the ending most people get.