Is doing a lifetime deal for a SaaS lead-generation tool a good idea?

It depends on the specific details of the lifetime deal and the SaaS lead-generation tool. Generally speaking, lifetime deals can be a good way to get a great price for a tool that you plan to use long-term. However, it's important to make sure that the tool is high-quality and will meet your needs over time. Additionally, you should consider factors like the company's track record and the level of support they offer before making a decision.

I voted "maybe" because i usually look for lifetime deals.
Offering LTD will be burden if everyone who has purchased the deal keeps using it.
But the reality is different, most people don't use their LTD.
So accordingly judge your offer, expect a medium usage for about 30% of total purchasers.

I voted "no" before fully thinking of it. But it will probably depend on what you store in database. If it's AI generated or a one-off thing that you throw to the trash after the fact (no long-term persistence) it seems okay to me.

For instance, my biggest cost on my own SaaS is the database hosting: the cost increases with the amount of requests / disk size used.

If you don't have constraints that binds the long-term usage of your tool with your own money, I would say it's safe to have a lifetime plan. "Pcloud" which is an alternative to Google Drive does that well: you pay lifetime but you know you are limited to N Gb of disk storage, they don't take the risk of losing money on the long term.