Is it mandatory for one to carry the original passport all the time while cross Liechtenstein to Austria for a day break and also carry the Driving licence and IDP?
Whenever you are crossing a Schengen border, you must de jure be in possession of a valid passport or accepted national ID card.
In many countries (I believe Austria to be one) you need to be able to identify yourself (passport or EU member state national ID card) if the police asks you to.
If you are driving, of course you must have a valid licence on you at all times.
De facto it is very likely for nothing to happen and nobody to ask. So you could get away with it if you want to test your luck. I’m not recommending it because the consequences can be a severe nuisance.