It's refreshing and pleasant when a client is willing to discuss things in good faith and find a reasonable solution. And it's sad that in my career it has ... never happened. I have approached clients, and clients have approached me on options for continuing projects - but the discussions have never reached a good outcome. These anecdotes to point out that yes, such options should always be on the table (if both sides can manage) but you can't rely that something like this will happen, until it happens.
I don't know, I've had tons and tons of clients over the 20 years I have consulted. Off the top of my head, 80% have been fine, 10% run in to issues now and then, but there's a hardcore 10% that will stretch you and stretch you because they can (I'm talking about paying NET 60/90 when the contractual agreement is NET 30).
If you withhold services, you usually lose that client. To be honest, that's not always a bad outcome, because a bad or slow paying client is usually the noisiest, most demanding and most unreasonable one as well.
I expect you value that client, and you should!