Most professional chefs have had a hollandaise sauce split in their time. The trick is not to panic, you won't need to start over again if you follow Paul Heathcote's advice.
The key things to remember when making hollandaise is that you must not over-heat it (that will cook the yolks) and that you should add the melted butter in a very slow trickle.
But don't worry if it does split, it's easy to bring back together again.
If you get scrambled eggs...Unfortunately, if your hollandaise starts to thicken into solid lumps - it's beyond repair. You have over-heated the mixture and the egg yolks have started to cook and coagulate.
You no longer have hollandaise, you've got scrambled eggs and you can spread them on your toast!