what happens when trademark owners have an active mark but abandon the usage of their mark for another type service without informing the trademark office.
I'm going to assume we are talking about the US, and these comments address US practice...
As to "what happens" as far as the registration is concerned, the comments above apply to US trademark registrations which require a statement of use and proof of use at periodic intervals. There is no requirement to inform the USPTO. You have to be careful about your assumption that they have, in fact, abandoned the mark. They may be using it on those goods/services elsewhere, or they may have temporarily stopped using the mark for one reason or another.
If we are talking about "what happens" if that registration is asserted in the UDRP, then there's something of a problem. One of the screw jobs of the UDRP is the lie that it "does not expand trademark rights". It certainly does expand trademark rights, because a UDRP panel will not question a registration that is still in force, even if there is reason to believe it has been abandoned.
On the subject of:
another service that's totally different
Whether it is "totally different" or not, is also grist for the factual mill.
But, yes, I've run into this situation a couple of times. The swash.com proceeding was one of those instances. Also, while not very well fleshed out in the decision, the fiesta.com proceeding involved a mark registered in various European countries for "tobacco products" which the Complainant had not actually used for tobacco products for a very long time (a decade or more). The Complainant then launched a new line of electronic cigarettes under the long-disused mark, and claimed rights back to 1973 for entirely different products.
http://www.wipo.int/amc/en/domains/search/text.jsp?case=D2015-0080
In situations where I see a UDRP complaint which merely asserts a trademark registration, and does not back that up with any actual use of the goods/services, then it is usually a red flag. The way that UDRP panels are inclined to deal with those kinds of situations is almost hidden in the decision:
"The Complainants, which bear the burden of proof, in turn, furnished no evidence that the FIESTA Marks were well known anywhere in the world, let alone in the United States (the Respondent’s home country) in 2008 when the Respondent acquired the disputed domain name. Moreover, the Complainants failed to provide evidence with regard to publicity of the FIESTA Marks and to the extent of their business activities in the United States. Finally, the Complainants did not provide any evidence that the Respondent targeted the Complainants or the FIESTA Marks at any time."
Unpacking that, rather than to dispute the validity of the mark based on non-use, panels are more inclined, in situations where it appears the mark was abandoned for its original purpose, to address under the "bad faith" element whether there was any reason for the respondent to know about the mark (i.e. since they don't actually sell products under the mark for the recited goods/services).