、。
If there are no accidents on the snowy roads, I think we'll be able to get back safely.
Literal
Snow-road [at-で] accident [subject-が] not-exist [if-たら], safely can-return [quotative-と] think.
A travel-safety prediction. ~がなかったら ('if there's no X,' 'provided X doesn't happen') is the past conditional of the negative ~がない — a hypothetical past scenario. 無事に ('safely, without incident') is an adverbial form of 無事 ('safety, being unharmed'), a formal/traditional concept originally referring to the absence of major events. 帰って来れる is the potential of 帰って来る ('come back, return'); note the casual drop of ら in 来られる → 来れる ('ra-nuki kotoba'), where the standard 来られる is shortened to 来れる in modern casual speech. This is a well-known ongoing change in Japanese.