I am guessing, after living in switzerland for 23years, but a locked lease of 5 years is only to say they can kick you out , with good notice that at 5years, for whatever reason. And should it go past the 5yrs, it is normally extended for the same period of time. 

So doulbe check the wordinging where it talks about ending the lease or giving notice. 5 years is abusive and Im certain its not acceptable acceptable anywher in Switzerland.

However, there must be a ariticle in the lease, that says you must give a 3moths notice if you want to move out, or if earlier, you must present 3 suitable rentees , where they either must accept one of them or they can not hold you to further time period. 

See with Asloca in Vaud, they have great website, just for starters, and if zour am member you can get some helpful advice, normally membership is like CHF 50- per annum.

www.asloca.ch/vaud/

Also lease agreements for UN or OGO non locally employeed persons, fall into a totally different category and can almost move out immediatly without much notice.  Owners and agencies hate to find this out later. 

5 year leases are rarer, but still exist in the Lake Geneva area, and a lot of them are indexed. 

Most flat leases are 1 or 3 year, renewable. Some of the 5 year leases do have either a 'diplomatic clause' where you can cancel the lease with 3 months' notice after the 1st year if you're transferred outside of Switzerland or you can cancel the lease once a year on the anniversary after the 1st, 2nd or 3rd year. It's rare to have a lease cancelled after 5 years, though, on the owner's part. Most are automatically renewed for 5 years or revert to a 1 year renewable from year 6. 

I would definitely study the lease to see how long you're automatically locked in for (always at least a year) and see when/how you could get out of it. As it seems like you already know, you can always get out of a lease in Switzerland if you find a replacement but, as you mentioned, that could be very tricky if there's works or a nuissance around. 

Thanks so much guys for the thorough answers, that is already a great help!