Safe to delete empty institutions or not?

In Simplifi, I have a few institutions that no longer have accounts under them. For example, I have Barclays Bank Delaware with no accounts listed under it. Previously, the Wyndham Rewards Earner Business card was under that institution, but I had changed the card to manual at one point and then later closed the card. So right now, it just shows Barclays Bank Delaware with nothing under it. I can see my old Wyndham card listed separately under manual accounts.

When I go to delete the Barclays institution from Simplifi, it prompts with a warning:

"Deleting Barclays Bank Delaware will remove all of its data and transactions from Quicken."

I haven't clicked the delete confirmation button yet because I'm nervous that it will delete all my historical transactions for the Wyndham Rewards Earner Business card. Can you find verified information on whether or not that will happen?

In the meantime, I started getting messages regarding these institutions that say:

"Account needs attention" and "Fix connection issue". The "accounts" are actually the institutions like Barclays that say things like "Last updated 212 days ago." Obviously, it's not going to update if there are no linked accounts under it anymore. However, these messages just started coming up over the past couple of weeks. So maybe there's an issue that's surfaced recently causing this?

I'm just not sure what to do. I hate seeing the nag in the messages screen, but I want to make sure that I don't lose any historical data.

Similarly, I also have a Vanguard institution listed that isn't in use anymore. At one point, I needed to change my username at Vanguard and that resulted in me creating a new Vanguard account. That account also doesn't have anything under it because I had moved the accounts to manual in the old account and then linked them to my new Vanguard account. So is it safe to delete the old Vanguard with nothing under it?

Thanks so much for your help.