I don't know if it's possible to tell you how many points. But the account will be on your reports for about 10 years after closing. And unless you have a lot of newer accounts, you shouldn't see that much of a difference when it does go away.
The biggest issue you may have is your utilization. If you have balances on other cards your util will go up. Depending on how far it goes up will depend on how low your score(s) will go.
To combat that you can see if you can get a CLI from one of your other CC's in an effort to make up for what you lost with Chase.
had this account since 1997 which is my oldest. this cc accounts for 15% of my total credit limit. my current fico score is 794. how much will this affect my score? my 2nd oldest is from 1998.
It will continue to report for 10 more years from now and will continue to help your history. Once it drops off, then your score could change depending on the TLs you open between now and then.
If your balances on each CC are under 10%, then you won't see a significant change. However, if you are carrying balances, then you may see a hit. Total your CC balances and divide it into the total CL (be sure to include this CC). Then repeat the calculation excluding this CC. If that percentage increased, your score will drop. But again, if your balances are in check you won't see a decrease.
Last impact may be mix of credit. So as long as you have 2 open revolving CCs and at least one store card after this closure, you'll be OK.