Sadly, and in my opinion your friends have acted in a fool hardy way, totally ignoring the rules that come with a marriage visa, what were they thinking ?
Everything was in their favor and yet they sought to ignore the rules that are applied and followed by everyone else, and now they seek to justify their position by hoping that somehow they will be able to get around the laws of the country, we may not like the system, but the system works if followed properly.
However, your friends are legally married in UK, you say in January 2008, and therefore, whilst the applicant overstayed beyond the validty of the marriage visa, the marriage in fact has taken place.
If they have applied for Further leave to remain, (you don't clearly state if they have done so, only indicated that they might have), should that application have been refused on the grounds of overstaying, there is little point in my opinion for the applicant to return to the Philippines to try and alternative route of entry, i.e. a spouse visa, a settlement visa for a spouse is only issued to an applicant who is wanting to enter the UK for the purposes of settling as a married person for the first time, the 24 months probationary period commences once the visa is issued, and not when the applicant enters the country, a fact many fail to notice until it costs them another £395.00 for extending it at a later date).
In this case, the applicant is already in the UK, has already crossed UK border, and is in fact now married, if the Home Office will not grant Further leave to remain, the Home Office will also have told the applicant in writing why they will not grant FLR and also what they must do, i.e. what is the validity of their status, they would not leave the applicant in limbo, what you have not told us about your friends, is the status of the applicant.
Its my guess, either your freinds have not applied as yet and have already been warned that they risk a refusal, or if they have, they have been told that the applicant has a certain amount of time to leave the UK, and there is a cut of date for this, and the applicant has been ordered by HO to leave the UK forthwith.
If not, then your freinds have not applied, and are still overstaying and seeking further advice before committing to such a move either way.
My advice is to seek the help of a specialist immigration solicitor, such as visiting the Immigration advisory service, and to put your freinds case before them, they can advise as to what representations can be made to the Home Office, they are known to not take any money in the initial stages and if the applicant is of limited means, very often they can take the case without payment, it could be that the Immigration advisory service may need to list a hearing to make a stay of execution of an order to leave the United Kingdom, this can be done and is often overturned once the facts have come before an immigration judge.
If your freind does decide to leave the UK on a scheduled flight, there is no immigration check on departing passengers in UK ports of departure, only a passport check to ensure the passenger is in possession of a boarding card, and that the boarding card is the same name as the passport, as far as immigration control is concerned, there is none in force, so the applicants departure is not going to spark any problem.
