It's idiomatic, I think, at least as far as whether we use a gerund here or an infinitive; English requires one, Greek the other.
For the grammar, first: an infinitive used substantively may sometimes omit the article.
See the LSJ entry for ῥύομαι and Smyth § 2038 and 2744
Verbs signifying (or suggesting) to hinder take both the simple infinitive and the articular infinitive. Such verbs may take the strengthening but redundant negative μή
αἰνέω can take a complementary infinitive: They allowed him to escape
, to give a parallel English construction.
The LSJ lists both a genitive and an accusative complement as possibilities with ἐκφεύγω (again, in English we can say, escape a place
or escape from a place