The phrase
Di melius!
comes from Letter 98 of Moral letters to Lucilius, original text can be found here.
The translation
Heaven decreed better!
is by Richard M. Gummere Ph.D.
More comprehensive piece of text (for the context):
...
For whether you prefer to observe other men (and it is easier to make up one's mind when judging the affairs of others), or whether you observe yourself, with all prejudice laid aside, you will perceive and acknowledge that there is no utility in all these desirable and beloved things, unless you equip yourself in opposition to the fickleness of chance and its consequences, and unless you repeat to yourself often and uncomplainingly, at every mishap, the words: "Heaven decreed it otherwise!". Nay rather, to adopt a phrase which is braver and nearer the truth – one on which you may more safely prop your spirit – say to yourself, whenever things turn out contrary to your expectation: "Heaven decreed better!"
...
I would like to know if translation will remain the same, if phrase ("Di melius!") is taken out of context.