Examples of what a smithing skill could do:

Whether online or offline, if any of your weapons are not at full strength, trained smiths would repair the weapons automatically.

At some point, smiths could even produce weapons, etc.

They may also be able to detect sabbing, and attempt repairing the weapon based on their level...

They would be able to repair your defense weapons even when offline so that your defenses are returned to full value as much as possible.

For attack weapons, they can be repaired after so many attacks, etc.

The repairs would only occur if there was enough gold to pay them. The smiths could repair a certain number of points per the number of smiths per 30 min.

Ex.
I am offline
I have 12 smiths (They can repair up to 12 points of damage every 30 minutes, if I have enough gold to do so...)
I get attacked and lose gold, soldiers, weapons take damage, etc.
Whether I win the battle or not, the smiths take action the next time the 30 minute count occurs.
I have invisibility shields and dragonskins damaged needing smithing, and enough gold to repair them.
My weapons sustained 11 points of damage per weapon type, etc...
The smiths will repair 11 points of damage on the invisibility shields and 1 point on the dragonskins.

No attacks through the next 30 minutes...

Smiths take action and repair the remaining 10 points on dragonskins...

I log on, and my weapons are at full strength.. (or as close to it as I had gold and smiths...)