Is there any other utility for ordinals except for nft /dig…

Yes, You can immutably record any type of file with 1sat Ordinals Protocol for future data evidence. Ordinal can be used for games as in https://championstcg.com/ or https://foxplorer.org/. I'm also exploring uses of Ordinals in Metaverses.

I have a question what if all the sats in the world is already used? What are the possible solution?

I've also asked myself the same question and I don't have the exact answer. We could theorize and debate about possible scenarios:

1. If we run out of satoshis just by using them in ordinals, I wanted to say that the protocol is super successful because the amount of available satohis is huge.

2. Unnecessary, useless, and worthless ordinals could be burned to reuse the satoshis in new ordinals.

3. Another open protocol could emerge in the future that is more efficient in the use of satoshis, such as representing complete accounts in just one sat, such as account-based blockchains.

4. Let the market evolve and different protocols compete, such as Op Return protocols with non-spendable outputs.