It's generally agreed that Roman religion was oriented towards orthopraxy rather than orthodoxy. Belief was less important than the correct practice of rituals. It would follow that Romans didn't think all that much about the afterlife. The observance of rituals was aimed at maintaining or improving Roman fortunes in the world (victory in battles, for example), rather than securing a comfortable afterlife.

Lucretius, however, gives us a very interesting viewpoint at the end of Book 3 of the De rerum natura, his philosophical poem on the nature of the universe. Lucretius lived in the last decades of the Republic, so he's right in your time period. The poem is one of the best sources for Epicurean philosophy we have. Epicureanism adopted atomism and argued that we no longer exist once the combination of atoms has been broken. Thus, death is nothing to us (since we do not exist after death and thus can't feel or care about anything).

Epicureanism argued that the fear of death was one of the major anxieties afflicting humans, and that this fear was unfounded since nothing survives after death. Lucretius gives a number of things people might worry about regarding death:

• That the dead are deprived of life's joys.
• The fate of the body after death (being concerned about what type of burial, if any, they will receive).
• The mythical sufferings of the afterlife (Tantalus, Sisyphus, the Danaids etc.) are false. But, they do describe the lives of some people (the Danaids represent those who are never satisfied with what they have and always seek more, for example).

The latter two in particular both imply a concept of life after death (so does the first, in fact, since the non-existent can't be "deprived" of anything, since they don't exist to lack it). The last is in many ways the weakest argument. It's a lovely psychological analysis, so to speak, of living people, but it doesn't really attack Roman fears because there is no evidence that they ever worried about the mythological punishments. It's likely that Lucretius was attacking something of a straw man here, because it's fairly clear that Romans didn't particularly believe in myths.