If he was there he did it.
(Má bhí sé ann do dhein sé é?)

If he had been there he would have done it.
(Dá mba rud é go raibh sé ann bheadh sé déanta aige?)

Ba rud é = It was thus
Dá m[ba rud é] = If it was thus - as in "if it had been thus". Dá makes it a closed tense, right?

Is there any other way of expressing thes kind of complicated conditional clauses?

When you arrive on Dublin next Tuesday, he will have been there.
Wen you arrivedon Dublin last Tuesday he would have been there.

Is the context in Irish in these cases more important than the grammatical mechanics?

GRMA!

quote:

If he had been there he would have done it.
(Dá mba rud é go raibh sé ann bheadh sé déanta aige?)

This tracks the English closely and still manages to be good Irish. But in general, note that Irish just does not have some of the compound tenses that English uses freely. If you start with this Irish sentence:

Dá mbeadh sé ann dhéanfadh sé é.

it would be equally correct, depending on context, to translate it as:

If he were there he would do it.

or:

If he had been there, he would have done it.

quote:

When you arrive on Dublin next Tuesday, he will have been there.

= Nuair a shroichfidh tú BÁC Dé Luain seo chugainn, beidh sé ann / beidh sé ann cheana / beidh sé tar imeacht.

I suppose you could also say "... beidh i ndiadh a bheith ann," but then it sounds like you're thinking in English.

Rinne mé botún cló. Recte:

beidh sé tar éis imeacht.