Well, its true that you have to spend spells on traveling, but if you had 2 spells you could cast that would give you "A safe place to sleep, and persist all you buffs for free", i am sure you would cast them.
Besides, if your a cleric of mystra, nothing will be able to stop you from using your magic to leave. If worst comes to worst you will just drop a antimagic field to suppress any magic holding you back. But its a valid point, what if you get caught somewhere without a way to get back to the temple for a while. In that case, you improvise, adjust and go with the flow. You might be a bit weaker for a short while, but you will still be a tier 1 full caster.