If 2) is found to be unenforceable then does that mean you also
weren't responsible for 1)? What process would a court go through?
The Court would determine basically if invalidating the provision that violates the law or public policy or what have you still leaves a remaining contract that fairly be said to reflect the intent of the parties. If so, the offending provision will be severed or reformed, if not, the entire contract will be invalidated. In most cases, a "savings clause" is mere window dressing that only matters is a really close cases where the intent of the parties is ambiguous.
(On the other hand, an "anti-savings clause" which provided that if any provision of the contract was held to be invalid that the entire contract was invalid, would probably be upheld even if the offending clause would otherwise have been severed from the rest of the contract.)
In this case, "2" is probably invalid because it is a "penalty" rather than a "liquidated damages clause" that fairly attempt to estimate difficult to quantify harm associated with a particular kind of breach of contract, since the amount owed exceeds any reasonable estimate of such a harm. But, eliminating that clause doesn't really undermine the intent of the rest of the agreement and any specifically proven harm actually cased by the late return could still be imposed by a court as damages for a breach of the deadline to return the leased vehicle.
Also, usually invalidating a provision of a contract is an all or nothing thing, but if there is reason to think that the offending clause is problematic due to a clerical error or mutual mistake, the contract can be reformed to reflect the true intent of the parties. Furthermore, sometimes statutes allow a particular kind of offending term to be modified rather than stricken (something that is called, somewhat derisively "blue pencilling"). For example, usury statutes which prohibit the charging of interest above a certain amount often provide that interest be reduced to the maximum amount allowable by law when it is violated, rather than invalidating a provision charging interest entirely.
On the other hand, for example, if the agreement were to lease a particular model of vehicle which only used leaded fuel (something which has been prohibited in Canada for decades and is thus illegal to lease or operate), because that particular model was the only one the lessor owned that was available to lease, the entire agreement would probably be invalidated. This is because the invalidated provision goes to the heart of and central purpose of the agreement which cannot be fulfilled in any other way.
For another example: I have a lease where on the addendum there is a
mistake. Instead of my name it's the old tenant's. Does this
automatically mean I don't have to do any of the items on the lease,
like mow the lawn? Obviously not, but how would the court decide?
This most likely would not invalidate either the lease or even the addendum. The lease would be reformed to reflect the true intent of the parties, because it was clearly and obviously a mutual mistake or clerical error.