Dried basil leaves instead of bay leaves

As another alternative, whole allspice berries have some of the savoury, earthy flavours of bay leaves (especially dry bay leaves). Having said that, dried bay leaf adds a pretty subtle flavour, so you could just omit them without any trouble: it's a nice flavour if they're present, but not going to wreck the dish if they're not.

I wouldn't use basil unless for a coconut-milk style Thai curry. But for Indian curry, there are also "Curry leaves" for sale in Indian food shops and markets which are delectable. Even their scent is intoxicating. They look like bay leaves but are larger.

No, this would be a bad substitution. Instead use cinnamon, in a smaller quantity, and preferably whole. Or leave it out entirely and rely on the other spices in your dish.

In my opinion at least, dried basil leaves are mostly flavorless. They certainly lack the sweet, fresh, minty flavors of fresh basil. They might lend your dish some complexity or slight woodiness like a Mediterranean bay laurel leaf from the plant Laurus nobilis. But even in European dishes, this seems like a poor substitute.

But in any case, the "Indian bay leaf" or Cinnamomum tamala is a whole different species, and probably what your curry recipe is looking for. Unlike the subtle menthol and tea-like qualities of a bay laurel, this leaf has a mild cinnamon scent. Thus a better substitute is cinnamon or cassia.

More generally, both these leaves have quite subtle flavors. In a dish with many different flavorful components, it plays a relatively minor role. It can often be omitted without a huge loss in flavor.