Check out Subscription class in Laravel Cashier. It has plenty of methods, such as valid(), active(), and cancelled(). You can also check user's status directly with the help of Billable trait: $user->subscribed() which returns true or false.
Thank you @cristo, I've got that working but had another question.
How can I get the next renewal date from Spark?
I've checked the database, it is not there - only "ends_at" is.