If the bed you last slept in is destroyed or mined, where do you respawn when you die?

In particular this is useful to know when one is exploring. I tend to put a bed down, sleep for the night, and pick it up again before I continue exploring.

In this case, where would I respawn if I died?

Perhaps where the bed was, or the bed I previously slept in, or my original spawn location?

After a bit of digging through the properties of the bed, I found this, hope this helps answer your question:

The bed is in no way tied to a player's spawn point - the game only checks for the presence of a bed at a player's spawn point when the respawn button is clicked from the death screen. The bed may be destroyed, replaced, reoriented, etc. and will still serve as a spawn point for players so long as it exists when the player tries to respawn. If a player's bed is destroyed or the bed is surrounded by solid blocks and the player dies when the player had set his spawnpoint there, a message is displayed saying Your home bed was missing or obstructed, and the player will respawn at the original spawn point.

Source

In this situation of placing a bed, sleeping, and then removing the bed, you would not respawn at that location if you died. You would instead respawn at the world's original spawn point. In order to respawn at a bed, the bed still needs to be there when you die. If your bed is removed or obstructed, you will respawn at the world spawn point with the message 'Your home bed was missing or obstructed.'

So, if you're just sleeping for the purposes of passing the night so you can explore in relative safety, there's no problem with removing the bed. If you are sleeping for the purposes of setting your spawn, you must leave the bed behind in order to maintain that spawn point.