In european airspace it is perfectly legal to fly 10 days with an inop TCAS (except germany and switzerland which only allow for 3 days). This is most probably reflected in the respective MELs (it is in ours).
You can look it up on the eurocontrol pages and of course your local aviation administration regulations.
cited from
http://www.eurocontrol.int/msa/galle.../MELUpdate.doc
Operations in accordance with the ACAS II MEL
The JAR-OPS 1 TCAS II MEL policy document, recently announced through TGL 26, has promulgated the ACAS II MEL Provisions. A copy of TGL 26, Section 2, ‘MEL Alleviation to Subpart K’, Page 16, which deals with the ACAS II MEL provisions, is attached, for information; it can be seen that a Class C, 10-day, ACAS II MEL is applied within the ECAC States except in Germany and Switzerland, where a 3-day MEL is applied.
The actual period applicable to an aircraft is, however, set by the National Authority of the aircraft operator. Operators need to respect their own National Authority MEL unless a State has set different criteria applicable to foreign operators flying in their airspace. Operating to a more stringent ACAS II MEL than Class C, 10-days, is of course completely acceptable.
If flying with an unserviceable ACAS II, then the altitude reporting transponder should be serviceable.
Operation under the terms of the JAR-OPS 1 TCAS II MEL has been agreed and accepted by the ECAC Member States.
The US Federal Aviation Administration (FAA) has moved to a 3-day MEL. This is applicable to US operators. However, if an aircraft operator operates an aircraft into the USA under FAR Part 129, and it is an "N" registered aircraft, the more restrictive 3-day MEL applies. If it is not an “N” registered aircraft, the operating rules of the appropriate operator’s national authority apply.